In most cryptographic applications there's a huge performance margin between authorized and unauthorized behaviour. If decrypting without a password is 10 trillion times slower than decrypting with a password, it doesn't matter if an attacker finds a 4x speedup from somewhere.
If I'm trying to make a timelock puzzle that will last 50 years, I've got much less performance margin - a timelock guaranteed to last "somewhere between 50 and 200 years" would be very hard to achieve - and yet, not very useful.
Meanwhile, if the decrypter has to be run continuously, it relies on being powered and working, and kept up-to-date with the latest improvements in clock speeds, ASICs and cryptography - when the people operating it could go bankrupt, or change their plans, or get hacked, any of which could reset the timer to zero.
So for important applications like "these secret government archives must be made public in 50 years, but no earlier" it's useless because any adversary who wants to prevent the release can knobble the decryption process to reset the timer to zero.
And for unimportant applications like "Grandpa's old diary, which he doesn't want anyone to read for the next 50 years" it's useless because who's going to fund 50-200 years of cutting edge ASICs for something so mundane?
And for short-term applications like "the gambling site will prove the dice were fair after the game is over" there are simpler options available.
If I'm trying to make a timelock puzzle that will last 50 years, I've got much less performance margin - a timelock guaranteed to last "somewhere between 50 and 200 years" would be very hard to achieve - and yet, not very useful.
Meanwhile, if the decrypter has to be run continuously, it relies on being powered and working, and kept up-to-date with the latest improvements in clock speeds, ASICs and cryptography - when the people operating it could go bankrupt, or change their plans, or get hacked, any of which could reset the timer to zero.
So for important applications like "these secret government archives must be made public in 50 years, but no earlier" it's useless because any adversary who wants to prevent the release can knobble the decryption process to reset the timer to zero.
And for unimportant applications like "Grandpa's old diary, which he doesn't want anyone to read for the next 50 years" it's useless because who's going to fund 50-200 years of cutting edge ASICs for something so mundane?
And for short-term applications like "the gambling site will prove the dice were fair after the game is over" there are simpler options available.