There must be a reason why the competitors are using the same network which is ethereum it's probably because creating the product under this EVM are best, there must be doing research before initiate and launch the product. So it's not the monopoly at all but it's all about quality, the best quality product ofcourse will rule the market and if there is another better network than ethereum in the future, i'm sure it will have more marketcap than ethereum because investors are smarter right now, they will buy something that valueable rather than just a hype