I think I know what you mean, OP, but it seems like most of the comments think you are just complaining about people saying “thanks” at the end of an email, or in general.

So forget email for now. This is an in person thing or instant message. Ending an email, even a short one, with “thanks” is fine and normal. But if you message me “please update that ticket. Thanks.” It has a more aggressive tone than you might have meant. It feels like you aren’t asking and so the “thanks” comes off as fake or even sarcastic. Maybe also a bit dismissive or distracted. Like this isn’t a conversation or even a request. I’m telling you what to do and walking away. It’s a bit terse. If you say “please update that ticket” and I say “sure thing” and then you say “thanks”, the tone is much different. That doesn’t sound bad at all.

Again, email is different. Emails are meant to be send and forget. The thanks at the end can even be read as a “thanks for reading”. I think OP is talking about something different, and I agree it feels bad when someone talks to me that way.

As for your actual question, OP, I can’t say I know why they said it that way, but I’d guess they mean no offense, like most people are saying. It could be a second language thing or they really are too distracted or busy to wait for your reply. They don’t want to get into it, they just want to check off that someone is taking care of that one thing