One-page-only is great for new grads and people with a few years of experience.
I’d expect someone with 10+ years of experience to use a second page. My résumé is about a page and a half. Old (but relevant!) job experience has already been cut down to a single-line description for each job. At some point, there’s just too much content for one page, even if you ruthlessly edit your résumé down and just give the most essential details.
10 years of experience is what, 2-3 jobs? Easy to fit on one page. Just adjust the font size and padding between sections from the time you applied when you didn't have any experience and needed to pad your résumé.
I suppose it could just be 2-3 jobs and fit in one page. But 4 jobs is not uncommon, and for me, the 4th job is what got bumped to the second page.
You could have an entire discussion about how long people should stay at their jobs, but I don’t think it’s unusual to see someone with 4+ jobs in 10 years on their résumé, and it’s not ipso facto a red flag. I also have a small number of non-work projects which belong on my résumé. People will also put non-industry work experience on their résumé.
I’d expect someone with 10+ years of experience to use a second page. My résumé is about a page and a half. Old (but relevant!) job experience has already been cut down to a single-line description for each job. At some point, there’s just too much content for one page, even if you ruthlessly edit your résumé down and just give the most essential details.