They own the means of production for the leading models but they're far from monopolizing them since the techniques are well known. At this point it's a matter of having a head start and lots of capital to pay for the data annotation and GPU time to train them. Others are playing catch-up but they're hot on their heals which is the biggest reason for them to continue spending like crazy to keep their leads.

For the non-bleeding edge they have a lot of competition with more competitors showing up every day.

The way this is playing out is not surprising, it's similar to any other technological breakthrough as it becomes commercialized. Eventually those means of production will become commoditized as well.