I'd like the same option with texting. It's a pain to fish my phone out of my pocket just to see a "thumbs up" emoji.

(First world problems...)

Thumbs up emoji can be considered as legal agreement (if you had previous agreements made same way), so it is no different than any other acknowledgment.

See case of farmer having to pay penalty for not delivering on agreement, agreed over a messaging platform with a thumbs up emoji.

If they didn't have thumbs up as an option, they'd almost certainly feel compelled to send an actual text to show agreement. Then you have to debate whether you need to send a text back to acknowledge their agreement. Thumbs up emojis are great! They mean: I'm happy for this conversation to finish now.

Why? It's like an ACK.

UDP vs TCP, might not care to know it was received. It may be evident/insignificant... later.

How it is different than if somebody responded "ok" or "sure" or any other similar message? Or is it also unwanted? How is the other side supposed to know that?

I wouldn't say it's much different, also unwanted in certain contexts. Perhaps not know, infer/make a judgement call. It's just as fair to consider it 'unreasonable' as it is 'assumed'; many things can be true.

The first world solution to their problem is Do-not-Disturb mode :P To keep the networking aspect: it's QoS! Helps me, can only blame myself for looking.