There are many more than 20 witnesses, just 20 are elected from 100's to run the chain. The more nodes you have the slower your chain and without on chain voting you end up with messy hardforks leaving the protocol static.

We have dapps that created "guest accounts" for users to login with things like FB/Google. Moving comments/post offchain until they get a blockchain acct can remedy the situation until we get lite accounts, then we can scale much easier with native hive tokens and instant account creation.