From what I understand:
Even though a Steem transaction is zero cost for the end user, it's still costly for those running Steem. Servers, electric bills, maintenance, the list goes on.
Steemit doesn't run ads or sell data, so they don't have the "advantage" that fakebook or twitter have.
It makes sense to have a cap on smaller accounts' transactions to reign in costs, however I'd like to see them be able to interact significantly more than 10x a day. Hopefully larger accounts will be able to delegate resource credits soon.
I can recommend this post: https://steempeak.com/busy/@taskmaster4450/steem-freemium-is-not-free