Everytime I read something on the life in the late '80 in the USSR, there's description of food shortages and similar occurences with basically every goods of necessity.
While I can somewhat understand a food shortage, I don't get why exactly such a country was unable to have enough, let's say, soap, for everyone.
Mostly it was because of inefficiencies in the economic/distribution system operating in the Soviet Union. This is a big topic but I'll try to summarise as best I can:
The soviet had a bias towards heavy industry and particularly in the Cold War era, towards military production. The industry thing was partly ideological, but also a hangover from the Stalin era where heavy industry was thought key to building up all other industries.
This meant less investment in consumer industries, including things like soap. It also meant the 'centre' was less likely to intervene to fix hiccups in the system, which was a common corrective mechanism used in higher priority sectors (sort of replacing 'invisible' market forces).
It also meant other sectors like agriculture were disadvantaged by the greater desirability etc. in industry. So for example they realised by the 1970s that all the 'good' workers weren't staying in collective farms, because all the good opportunities were elsewhere. This meant the people you needed to improve the quality of work/labour in the kolkhoz weren't there any more.
The planned/controlled nature of the economy made it difficult to satisfy consumer demand. Since consumption rates were part of the calculations/assumptions of the production plans, this impacted how much was made and of what. So if someone at Gosplan got it wrong and more people in say, Novocherkassk, needed soap than was expected you could end up with mountains of soap in Moscow instead of where the demand was.
The actual distribution and retail networks weren't too flash either. Even simple things like getting grain from the fields to shops ended up with enourmous wastage with grain rotting in transit. Products people wanted were in warehouses instead of in stores. And so on.
Labour productivity was awful. Basically the amount of time/cost for a Soviet worker to product an item was higher than it should be. This adds to the inefficiency and low production rates for certain consumables.
The Soviet party-state knew this was a problem - the people told them so at considerable length over the decades. There were an array of experiments and reforms intended to correct the issues with the economy, but none quite stuck. So for example there were the "Kosygin" reforms (which were really the Liberman reforms but anyhow) from about 1962 to 1967. These reforms/experiments all had similar programs - enterprises being allowed to allocate their own funds to some degree (be that as incentive funds for workers, investment in new gear for the factory or what have you), enterprises being allowed to form their own links with distributors/retailers and different ways of quantifying/setting prices of items in an attempt to improve incentives to make/sell said items efficiently and selling stuff people wanted.
A separate 'stream' of reforms/experiments centred on attempting to improve the central planning/allocation mechanisms. This included attempts to form enterprises into combines to try and achieve vertical/horizontal linkages. Or attempts to use better statistical or mechanical methods to handle all the information generated and needed to plan the economy, such as through the use of computer networks.
Quite why all these experiments failed is a mixed bag. The standard explanation blames the party-state or bureaucracy's conservativism and sabotage. This is too simplistic in my opinion and ignores the fact that the same 'conservative' elements kept trying all these reforms and experiments even after they were 'defeated'.
Perestroika (later in the 1980s) tried to change this system (again) but in some respects didn't go far enough. The semi-planned semi free market created oddities, so some businesses couldn't operate properly together or items that could be gotten cheaply due to price controls were sold in free (or at least more free) markets elsewhere. They also had to deal with disruptions resulting from the collapse of the Eastern Bloc, where certain products and inputs had previously been imported from.
Here is a post I wrote recently about the shortages, more so about their scale, type and chronicity:
https://www.reddit.com/r/AskHistorians/comments/3or18c/shortages_in_the_soviet_union/cw1nizx
Now, references:
Alec Nove, 'An Economic History of the Soviet Union 1917-1991'. Anything by Nove tends to be pretty good though.
Archie Brown and Michael Kaser's collections 'The Soviet Union Since the Fall of Khrushchev' & 'Soviet Policy For the 1980s' both have good detail on what was going on with the economy and their systems at the time (being older texts, it is contemporary analysis though).
On the computer network/statistical reforms there is Slava Gerovitch's 'From Newspeak to Cyberspeak' (not a technical treatise but has some technical aspects) and Martin Cave's 'Computers and Economic Planning: The Soviet Experience' (which is very very technical). IIRC Abraham Katz's 'The Politics of Economic Reform in the Soviet Union' also discusses experiments and proposals for new pricing systems, the reformist efforts by statisticians etc.
As referenced in the linked thread, Stephen Kotkin's 'Armageddon Averted' and Archie Brown's 'The Gorbachev Factor' cover the perestroika era.