GoTG Vol. 2 takes place only a couple months after Vol. 1 and Dr. Strange covers the same as at least a couple other movies, so they have been playing around with the timeline a bit more lately.The previous two cinematic takes on Spidey couldn't wait to get Peter out of high school, so I guess it makes sense to try something different. I don't think it really fits in with the MCU's generally progressing in real time (with the occasional exception), but whatever.
I don't mind them keeping Peter in high school for a while, it's a nice way to make him feel unique in the MCU.