In The Fall of Berlin 1945 Anthony Beevor brings up the idea that Hitler's refusal to surrender or attempt to escape as well as things like the Nero Decree came from Hitler's excessive self-identification with the German people. The thinking goes that he saw himself as an avatar for Germany itself, and since he would rather kill himself than surrender that Germany ought to be the same way.

It's kind of an interesting idea, but I think there's also an explanation that doesn't require guessing at the internal state of a guy who was (by this point especially) kind of off the rails mentally:

Hitler and most of the rest of the top Nazis understood that surrender was going to mean their trial and (probably) execution. Even after it became clear that Germany could not win in any conventional sense many of them held out hope that they could bring about some kind of negotiated peace that would leave them in charge or at least keep their necks out of the noose. Obviously these hopes became increasingly more fantastical as the war approached its conclusion, but it's not like the Nazis were really known for their compassion.

As far as what the average soldier was doing, there were a couple of different factors at play;

SS members fought to the death both out of a sense of fanaticism and because there wasn't really much of an option otherwise. On the eastern front especially, having an SS tattoo was basically a death sentence. Given the choice between an inglorious death or a chance to go down fighting many chose to go down fighting.

For some German soldiers the choice to fight even after the war was clearly lost came out of an understanding that the longer they held out against the Soviets the more German territory would be held by the western allies at war's end. Even Germans who had no love for the Nazis had no desire to see Germany overrun by the red army.

For some it was simply a matter of practicality. The Nazis took a very hard line on the subject of desertion or surrender, especially as the war was clearly lost and more and more of Germany's forces were half trained boys or old men. Military aged men caught behind the lines without a pass were subject to summary execution. Surrendering and then being caught after a successful counterattack would also likely mean a shot to the back of the head. The more fanatical elements understood that many of their soldiers were not terribly interested in dying for the cause and so they took steps to prevent surrender.

Even with all this there were lots of soldiers who did surrender, especially in the closing days of the war. The highly trained professional military that Germany started the war with was basically gone by 1945, and quite a lot of their soldiers were half trained militia. The Soviets went into the battle of Berlin with sizeable stocks of Panzerfaust rockets that had been taken off of Volkssturm members who surrendered without firing a shot. In the west the situation was even more stark, to the point where Stalin was concerned that mass German surrenders were a prelude to a double cross by the western allies.

Hope this helps, most of the information is from Beevor; but I could probably think up some other resources as well if you're interested.