Because their long term military strategy changed.

Conscription makes perfect sense if you're setting yourself up to fight a defensive war. E.g., Finland's entire military is more or less built for a defensive war against Russia, so they conscript.

Because they built it into their long term strategy, like I said in my original comment.

Germany used to conscript, because there was this thing called the USSR that represented a very real and existential threat right next door. Then that stopped being the case, so their long term doctrine changed from defensive to expeditionary, so they stopped conscripting.

Given that expeditionary wars in the middle east are becoming a bit faux pas, and "being invaded by your neighbour" is back in fashion, I imagine more places will shift doctrine again and conscription will start seeing a return. Then again it might not because of how fundamentally unpopular it is with the population.

It's certainly a bad idea to rely on conscripts to make up the bulk of your fighting force. It's not a totally bad idea to have a population of fighting age citizens have had some basic military training and know which way to hold a gun. Countries like Finland or Switzerland have a more realistic view of what they may need to do if things ever got bad on their eastern front.

For the UK we'd have probably resorted to our nuclear deterrent before we consider putting conscripts on the front line.