Yeah you're quoting steam numbers. Steam might have grown 4x in the last decade, not PC gaming.
And who's buying physical copies these days? It was a very different story in 2010-2015.
It's only natural that a digital game distribution platform like Steam's user base grew (of course Steam's quality also helped).
Talking numbers...
2015 -> 1.9bil mobile vs 1.1bil pc gamers.
2025 -> 3.2 bil mobile vs 1.8 bil pc gamers.
For every 1 new pc gamer in the past decade, there were 2 new mobile gamers.
Also, most mobile gamers don't play on PC, while a lot of PC gamers do.
That tells you all you need know to realize that mobile will stay ahead, despite being more saturated.
Pc gamers are perhaps not dying out as I joked, but my main point stands, phones dominate