Do you make your excuses to leave a text conversation?

I never have. Unless it was a question I just came back to the conversation whenever I could. But recently I’ve noticed people signing off like they’re ending a real life conversation or telling me someone came to the door so they disappeared for a bit.
I mean I wasn’t dragged up and I’m generally a polite person but I find it a bit odd. It’s not like life isn’t continuing until the other person gets back to you..why do I need to make an excuse if I don’t reply straightaway??