I don't find anything wrong with 5E being so dominant. If other games were worth being more popular, they would be. The designers could make changes if necessary to make their games more popular if that level of "popularity" really mattered to them... publishers could advertise more if a higher popularity than what they currently have was that important to them... players who liked and played those other games could spend more time advocating for them and running games of them for people who didn't know about them if higher popularity mattered that much.
I'm of the opinion that once you reach a certain level of scale... any single individual voice ceases to matter. And thus one or two people saying "X should be more popular" is a meaningless statement, when you would need thousands, tens of thousands, hundreds of thousands of additional people out there to actually make something "more popular". If they aren't there, then it means 'X' is only as popular as it needs to be right now. So don't blame Dungeons & Dragons 5th Edition because (general) you, as an individual voice, can't find anyone willing to play your Legend of the Five Rings game since they only want to play D&D 5E. That just means you haven't done enough to make the idea of playing Lot5R popular enough to get others to sit at the table with you. It happens. And lessening the "popularity" of D&D 5E won't suddenly make your Lot5R table worth sitting at.