New entrant offers incredible product or service, customers rejoice.
Competing products, pale. De facto monopoly is established.
Time passed, maybe a new board and CEO, maybe not.
The now monopoly starts exploiting their dominant position by charging more for worse quality. For some time the monopoly will act as a moat for this behavior.
Customers no longer like the incumbent and a gap is opened that other companies and startups can attempt to shoot through.
Once one succeeds the cycle starts over.
Since someone pointed out this pattern to me I've tried to notice companies that don't follow it. It seems pretty common. Overall though, products and services in the market are still often good. You just have to be careful to buy them from the company that is still rising rather than the declining monopoly.