In reply to Unai.

That has issues, mainly the fact that by making installs asynchronous, activation would need to be blocked until after all the installs take place. Also, what does the post activation page look like? If you are on the recommended tab, should that be cached with your recommended plugins when you install? Should you see a notice of "recently installed but not yet activated plugins".

This was absolutely considered, but the can of UX worms here is much much larger and it's also not what the majority of end users need.