Plenty of cheap stuff is a consequence of companies interested in people's money and, yes, presence of at least nominal competition between providers (i.e. they can be essentially a cartel, mirrioring each other exactly, but each still wants to step into other's money supply and retain its own). Choice for customer is present but also equally nominal.

In deficit economy, economic agents aren't really interested in people's money, and competition is between consumers - who'll bid higher and offer something of real interest to provider. So providers hoard stuff and there are long lines.

Benefit for public is not a boolean, it's a spectrum. Lots of cheap poor stuff readily availible is better than having to compete for stuff, but less good than having choice between cheap poor stuff and more expensive better stuff, for example. For the latter, you need non-nominal competition and providers having to compete whithin the market, not outside of it, and also each individual provider having infinitesimal effect on whole market.

"Companies optimize to make as much money as possible, which is why there is cheap stuff" does not logically follow. I get what you're saying, but it's not related to the concept of companies trying to make as much profit as possible. Some will simply chase higher profit margins.