Despite popular belief, Americans actually do like grappling. I dont know why people keep pushing this narrative.
America was very receptive to MMA from the start, which was grappling heavy (literally brought over by the Gracies and shortly after infested by folkstyle and shoot wrestlers).
Wrestling is a core component of American scholastic sports, and USA is one of the major hubs of wrestling. If Americans did not care about wrestling, it would not even be an Olympic sport anymore.
America is also a major epiccenter for BJJ and submission grappling. Pretty much the leader in it along with Brazil.
In addition, just from watching MMA people clearly do like the grappling exchanges. People like submissions. People like GNP. People like takedowns. People like clinch knees and dirty boxing. We can observe fans cheering for it.
It's lay and pray and wall and stall people do not like.
As for the question - kickboxing and Muay Thai do not have powerful promotions to push them. One is based in Asia and has limited ability. It took the UFC a long time to get people to like MMA and they needed very good promoters (Dana White is very good at his job even if he is a dick).
To get the point across - you could just as easily ask why do people like the UFC but not the PFL or Bellator when it was around?
The answer is simple - people like the UFC not MMA. People like Coca-Cola and Pepsi not just cola. People like NBA and NCAA not just basketball. etc
MMA is not popular outside of the UFC in the United States. So the answer why MT/KB is not popular is because they do not have a good promotion to push it. Glory and ONE were not capable of doing so in the US, nor are they based in the US which heavily limits their ability also.