[simne]

Because of scale factor. LG, Philips and Samsung because of large scale production, selling screens really very cheap, much cheaper than could small scale factory.

Equipment to produce screens is not something from other world, they are not cheap but achievable for business, but on small scale will not be cheaper than priced LG or Philips screen, even without considering taxes and fees of marketplaces (could add 2x-8x of cost).

If some small factory will try to enter market, it will immediately become bankrupt, because nobody will buy more expensive than from LG or Philips.

Exist possible exceptions - some Industrial or Space or Military applications (or for example, Medical), where customer have very specific needs and could pay additional money for them.