Lack of capital investment killed small businesses. Everyone now has to pay a tax penalty to take your earned capital and invest it into local main-street businesses. This capital instead, though 401k, goes into trans-national firms.
I think that the lack of capital investment you're describing can be thought of as a particular instance of the economy of scale (at least, broadly construed): larger and/or conglomerated companies, prima facie, have to depend less on capital injections.
i cannot upvote this enough. The regulation has very little if anything to do with the closure of the vast majority of small businesses. Access to larger/more efficient companies that provide better service to cost has killed the demand for the services that small businesses provide.