Think about the thousands of avatars stored in the database all roughly 50, now image the size of the database if they where all 150k which is three times as large.
The limits there for a reason. Other than bogging down the DB with (sort of) large images, its also for the dal-up users.
if £10,000.00 magically appeared in my bank.. I still couldn't get a connection faster than dial-up, and this is the case for many people.
It's not a matter of choice, its the simple fact that its impossible.