The pictures you have linked are not dug-in tanks, but bunkers using tank turrets. This was a way to make use of the turrets of tanks that were otherwise obsolete or unserviceable, and was a logical way to arm defensive positions. Whenever armies had the time and resources to build proper defensive lines, tank turrets were often found to go into them. In Normandy, the Germans had scores of obsolete tank turrets built into standardised bunker designs.

Tanks were occasionally dug-in, but this was usually for a specific reason, for example the Red Army dug in tanks in the second line at Kursk, to better enable them to absorb a German attack in the featureless steppe where it was difficult to hide. But this was really only a way to deploy them initially: once the battle reached them, they were to resume mobile operations. We have seen similar (mis)use of tanks in some of the Middle East wars, notably the Golan Heights in 1967.

To dig in a tank is to misuse it: the whole purpose of tank is to give its gun mobility and protection. To dig it in is a waste of the resources that went into its construction, is a dubious use of its crew, while a field or anti-tank gun is easier to conceal and has a wider potential range of fire.

Not uncommon at all.

There would be a couple of reasons to turn a tank into a bunker.

Firstly, simply if the tank is too obsolete to be viable on the modern battlefield. In the short term, simply bury the tank in order to give it the smallest target possible, just the turret. By keeping the hull, though, you may be able to keep some of the power functions such as turret traverse or radio going, by use of batteries or engine. I've seen this both in WW2 from Germans and Soviets, through the Arab Israeli wars, to former Yugoslavia. Or, if the tank is broken down and can't move under its own power.

The next option is that it makes a purpose built fortification cheaper. Dismount the turret, place it on the concrete. This obviously is a more deliberate use, and is more likely to be centrally planned. Again, this is not unique to WW2: The Swedes in particular made it a matter of policy that when a tank was taken out of service, it's turret was placed on a fortification for either coast or airfield defense. More so, those turrets would be replaced with new ones as later tanks went out of service, so the fortifications would always be a generation behind. Again, though, this is usually a matter of using obsolete tanks. Or, in the case of captured French tanks in WW2, often a turret would be place on an Atlantic Wall fortification, as the Germans didn't really want to use many of them.

Finally, there is the rare, but not unheard of, use of modern turrets in fortified positions. About the only example I can think of off the top of my head is the use of Panther turrets in Italy. I've a scanned archive document somewhere which states that they are small, hard to hit, and quite lethal. However, like any fortification, once identified, they will eventually be reduced, and, frankly, given how cramped and lacking in space for ammunition a Panther turret is, I find it questionable if it was a good use of resources to put the gun, optics and steel plate into a little pillbox.

So, TLDR version: Not uncommon, and usually sanctioned at the unit level (for dig-ins) or Theatre level for purpose fortifications.

The German Army build several types of those. The first picture is a OT-Stahlunterstand mit Pantherturm. The Germans build several types through the war, the pillbox could be made out of steel/concrete or wood stands. These scans 1,2 show the concrete base of the turrets, in this case the Panther turrets. They vary in size and would sometimes have a shelter for the crew including beds, a stove and a generator for the rotating turret mechanism. Besides Panther-turrets, the Germans also build Tobruks with other tank turrets, like the Pz 38(t), Pz II or French R-35 turret

For more information on the subject you could check out:

Panzer Tracts No.21-2 Pantherturm I and II. By Thomas L. Jentz and Hilary Louis Doyle

A little reddit help for you, if this allowed, because you mentioned your text box looks like spam.

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The Germans would dig in tanks that were no longer mobile. The Italian "heavy" tank P40 was produced for the German army but due to a lack of engine production most of these were delivered immobile so they would be dug in around Italy, or have the turrets removed and placed like those in the pictures you linked.