It's not that difficult, it's just incentivized in our not-so-free market. Big companies can afford lawyers and lobbyists and they get all the best tax breaks and subsidies. Small companies, not so much.
each one of them brings variations to the base product flavor but no budget to implement them
Yep, because the base product is designed for the large clients.
It's all incentives to target big companies. Why do you need permissions and user account management in your software? Because you're dealing with 20+ people and you may not know everyone in your company and if they can be trusted. Why do you have a base product that requires at least 10,000 database items in it to be useful? Because the big companies have that many items and they've got a monopoly or oligopoly on the market.
I once proposed to have a sort of web excel with security controls and a way to let authenticated guests to work on a subset of cells as a way to move small businness online leaving control to them of their process implementation but couldn't find a sponsor.
This is actually what should and would happen in a free market. The majority of companies are not very large; most of them have a bit of extra cash to invest in a tool like that. There is a definite market for it. But why isn't that market pursued? All of the above incentives mentioned above.