Unless they make charging for mobile games outright illegal profit in mobile gaming is probably here to stay, so I don't think they're ignoring it as much as they're not too worried about it.

77% of the US owns a smartphone as of February 2018(http://www.pewinternet.org/fact-sheet/mobile/).

https://store.steampowered.com/stats/content/

https://twitter.com/GamesWeekMelbs/status/1054539574091767809

http://www.vgchartz.com/article/276688/ps4-vs-xbox-one-vs-switch-usa-lifetime-salesapril-2018/

US represents 14.4% of the data usage through Steam in the last 7 days, and Steam reported 90 million active monthly users in October 2018. 14.4% is 12.6 million, but Steam isn't all there is so let's assume Steam has a 33% marketshare in US (probably below any estimate you'll find, but let's roll with it). That's 37.8 million PC gamers in the US. I know that data usage might not be an exact indicator of how many users there are in the US, but it should be an indicator.

Lifetime sales of PS4's and Xbox 1s was up at ~45 million as of April 2018. Even if we assume everybody here is unique with no overlap that still doesn't get us to the estimated 250 million people in the US who are estimated to own a smartphone. How many of them are interested in gaming?

https://www.statista.com/statistics/234635/number-of-mobile-gamers-forecast/

Apparently fuck-loads. I can't access the source and it doesn't seem to distinguish on smartphones, but that's still a very high number.

So I do not think these companies, or investment articles, are being idiots. I think they're making a smart but unpopular expansion into a large growing market. Sure, the market might experience explosive shrinkage (yeah, top-tier terminology here) due to legislation closing some forms of monetization, but there should still be money to be made.