i think you guys are mistaking him with the popular gays like tyler oakley, troye sivan, connor franta, joey graceffa.
those were the ones getting the big numbers. mark and ethan were part of the gay couple vloggers club, and they never reached that level of fame and popularity. they never made the numbers guys like tyler or troye did. the gay couple vloggers mainly stayed within their bubble, while the popular gay youtubers were making content with the popular straight youtubers, increasing their numbers even more.
youtube is also not as kind to gay youtubers. they will be more likely demonetized for doing the same or even a tamer video that a straight youtuber would do. demonetization doesn't always mean 0 money, but it limits the amount of money you'll be making from that video. lgbt channels are also more likely to be hidden from anyone who has their settings to enable restricted mode, which didn't used to be an easy thing to find to turn off(it used to be hidden at the very bottom of the page, and couldn't be reached on any page that was infinitely scrolling, so you had to be outside your subscription page to see it at the bottom. now it's just on your main pfp settings). mark and ethan once even made a series of tweets when they found out mark's channel was hidden from searches and most of their videos, which were completely harmless vlogs, were completely hidden when restricted mode is enabled. imagine how many viewers and subscribers they lost from people who never saw their content because their accounts were restricted.
also, mark might seem like he lives humbly, but he doesn't. moving ain't cheap. and it's not like he's moving within the same city or state. he's moving halfway across the country, to california, which is an expensive state. buying groceries, which are going to be more expensive just for his diet. he has a dog, which don't forget required major leg surgery couple years ago. he's into photography, meaning he likely spends a good amount of money on things like cameras and lenses. and don't forget he just bought an $11k car that, based on what he said on his video, is not considered a good car. chances are it's a gas guzzler, which is gonna be an added expense.
if he was fine money wise, he wouldn't have a patreon with a $30 subscription. he's not struggling, but he sure as hell ain't swimming in it