Can anyone think of a reason for this drain pipe to be so high?

Apologies, it’s a mess down there. We’re going to clean the heck out of it before we actually install the sink!

https://imgur.com/a/JoFEoxh

Got a new kitchen sink, and I found out that this pipe is barely in the way, by about half an inch. Does anyone know why a drain pipe would go this high up? Is there any reason I shouldn’t replace it with something flexible, or move it back so it fits under the sink?

The pipe is about 2.5″ wide, I think. I’m pretty sure it connects to the washing machine, whose drain pipe is about a foot higher.

Unfortunately I can’t ask the guy who made it–he passed away before we moved into the house.