You only want this because your own personal workflow style is to write short comments that need very little thought or editing.
Whereas the more contemplative of us want to write, think, rewrite a bit, check our work, add URLs etc. On some platforms, especially mobile, the backspace and enter key are so close you hit one or the other by mistake all the time.
This is a "fail-deadly" configuration. In exchange for a tiny bit of convenience for you, we are stuck with a great deal of "Aargh, damn it", thrown off our train of thought, and having to struggle back to "edit comment".
To add insult to injury, a 5-minute timer is now ticking. No big deal to a drive-by like yourself, but us contemplative folks often are not able to finish our comment properly in those 5 minutes. Now we must go through yet more rigmarole to copy our failed comment, paste it to a new comment, and delete the earlier comment shard.
Even worse, in those minutes, a person often comes along and replies to our comment shard - and lacking our full meaning, their comment is often redundant, unconstructive or rooted in a wrong inference - and now when we fix our comment, or delete the comment shard and place the fixed comment below, the comment thread makes no sense whatsoever.
So the detour you must make when "press enter to post" misfires is much, much worse than the detour you must make when you hit enter and it moves down a line or does nothing. Hence, "fail deadly".
It also rewards and encourages flash/emotion/snark comments, and discourages thoughtful ones. That alone makes it more suitable for places like Youtube comments, not here.
Kill "Press enter to post"