"Of course general purpose CPUs exist, simply because we call them that way."
the wisdom of those real world coders gone from this world is thus. a jack of all trades, is a master of none.
this means simply that a general purpose FPGA that can modulate it's functions can do a lot of different things but not at the same time, and in etched hardware the trade off is having dark silicon for all the tasks a true jack of all trades cpu can do.
for instance, when i was doing video games all day the more games i played in diveresity made it harder for me to 'master' a game. but the one game i mastered i could play at the 1% level rank of 800 out of 1000 on a game ladder. and because doing the same thing over and over made me good, i rebelled a bit and would have to rotate my build orders and strategy selection, though i once took a good undead vs human 1v1 staretegy that requires building an item shop first and when the necesary tech of the item carry ability is done to send the ghoul out hunting the enemy base, equiped with a rod of necromancy for the hero and pick your best mercenary hero, i used tinker. then you focus on killing one militia and try not to let the ghoul die and use the rod of necromancy and a pocket factory to harass, only a human who goes fast footmen with a MK can beat this strategy so i took it to 13:1 after which i got bored with it.
anyways what i mean is because i played so long and hard i got really good at the game. but i like a fpga had to map the circuits to get it to work. i had issues and quit playing games, though not forever. i played the game again a bit later and it took me a full month to get back to doing the same gameplay at my highest level, but then i quit it was too hard on me. i am very much like a fpga in that my functions can be practiced until i am good at them/set the optimal gate array, unlike a fpga the base ability to do stuff takes time for the programming to work right. even then i was only 800 or so of 1000 ranked players. (at the time they had around 30,000 players for the game online durring normal usage times) like a fpga i was reoptomized for whatever i was doing, and so had a memory effect at the tasks i repeated frequently.
anyways, a jack of all trades is unable to truly master something, that is the trade off for designing a chip to be that way, you can make a processor that does one thing well like gpus, you can have a fpga if you anticipate needs to switch its abilities, or you can make proper dark silicon that is switched on only when calls for that function are anticipated/occur. so really a general processing unit does exist and it is just inferior to specialty designs, because of how it is built to do everything a processing unit need might based on predictions of how a person will use it.
in other words a dark silicon design is like a RV it can drive it can be slept in it can tow a car if needed and has a toilet and stuff, they cram everything you need in one box albeit at a price. of being bigger to accomadate anticipated needs. a fpga is like an autobot in the shape of a smaller rv, in that it can reconfigure itself to the needs and thus is lighter and more compact than the dark silicon. finally there is the gpu version this is not an autobot nor a rv but rather a car with a rocket on it's back. it takes you from home to shop etc, but at speeds the autobots and the rvs can only dream of (ignoring the possibility of spaceships/starscream), but it can't do everything else it is only able to move you fast from point a to point b.