Like I say, in business there is no cheap or expensive. There's worth the money, or not.
Yes, Oracle costs money. But so does "rolling your own". How much of their VCs cash has say Twitter spent doing that? Yes, Oracle "locks you in". But your own legacy code locks you in whatever platform you've built it on.
In the specific case of FlockDB, that's actually not the case as the shards are modular. SQLShard is one implementation. There was an experimental Redis shard implementation, as well. You might be both overestimating the cost of building things like this and underestimating the enormous drag of using closed source components in these systems. If you've personally built online services this big with Oracle, well done. What did it cost?
Once you have hash joins, shards start to look awfully restrictive compared to partitions... MySQL (et al, I don't know about FlockDB) can freely shard because they're not losing functionality they don't have in the first place.
Maybe I'm not a good example because I've mainly worked in financial services, but nearly every Oracle project I've worked on has been wildly profitable, and most have been at the level (in terms of transactional throughput, and in terms of features that were cheaper to buy than build) at which there are only really two choices, Oracle or DB2.
Vendors highly optimize for your case, and you find that their solutions work for you. Not a surprise. Different constraints and different requirements produce different solutions. Nobody is saying you are doing financial services storage and processing wrong. Why are you so insistent experts in a totally different field are doing their jobs wrong?
What scale? How many concurrent users of your specific site break MySQL, and how many concurrent users do you have? Not answering or considering those questions is what leads to premature scaling.