There are 3 main reasons it has not gotten bigger.
The rules are hard to find, buried in obscure forums and chat channels.
Drastic changes can and have happened very quickly with no investor input, costing people thousands of dollars.
It is vulnerable to outside intervention due to the small core group of 100 witnesses that run the network. (It's the opposite of decentralized, and the general public has no reason or way to benefit from helping the network).
Until these things are remedied, big investors will stay away.
To make it worth the risk these things need to happen.
Clearly defined and publicly posted rules.
Changes only happen over a period of months after much discussion, simulation, and pre-testing.
Decentralize the network, by allowing creation of more groups of 100 witnesses. (this needs to go meta, 100 groups of 100 witnesses)
Put some proof of stake type benefit back into the wallet, and give regular users a way to support and profit from helping the network.
Just my two cents.
The number of witnesses is set by the voters, so it could go as big as you want if there were that many trusted players and people wanted to elect and pay for that many. It is already far more decentralized than Bitcoin where three companies sign over 51% of the blocks and therefore control the network. With Bitshares all nodes are limited to signing the same % of blocks, so that's already limited to a few percent max per elected witness.
It's coded that as many as 1001 witnesses can be elected at the same time to produce blocks. I didn't see the reason of each "group" need 100 witnesses.. can you elaborate?