Whether I like it or not, it seems that the modern chat client (e.g. Discord or Slack, not IRC) has developed the expectance that you "react" to chat messages as they happen - because there's a mental model that you're literally "chatting" with someone, and not showing you're listening is a faux pas, so the minimum effort response is a "react", especially thumbs-up just to mean "I saw this message and have no further comment on it"

You can of course chat in email, but it's unusual, there's usually a higher bar to responding; it would be madness if every email had everyone else in the chain send another email saying "I've read this", so that's not what people do. I only see "I've read this" emails if the penultimate email concluded the topic and that was all that's left to say. Hence why it's unwelcome to bring the habits of chat clients to email.