Dh never drinks all his tea/coffee

[ItsTricky]

He always has to leave a little bit. I always have to remember to empty his mug into the sink before putting into the dishwasher or I get splashback. Most of his family leave a bit too. Dh has no explanation for this other than 'It's what I've always done'.

I don't get it. aibu to think this is daft?

Maybe there's some perfectly logical reason I'm totally missing

I do it because I often don't get a chance to finish it before it gets too cold to enjoy. Tea or coffee that has gone cold is vile.

When I'm at home I usually give it a quick zizz in the microwave to warm it up so I can finish it..

My mum always does this with tea and coffee. I've no idea why. I sometimes leave a little bit of tea whereas DH always drains his cups. Sometimes I am slow drinking my tea (getting distracted by DCs for example) so when I get to the end it's a bit cold.
My dad is prone to having a cup of coffee and forgetting about it, then finding a cold cup of coffee lying around.