DAPPS and L2 query

Will most of the dapps will end up using L2 by default in future ? If so – why uniswap and others aren’t use it by default ?

Like how we plan to have multiple eth clients available and user can pick&choose – do we think – dapps will also enable this route for L2s too ?( showing various L2 routes and also possible gas fees optimised suggestions ? )

Future i mean – till we get into fully working POS and sharding in place.

How this will impact overall user onboarding journey ?