I'm sure that helped its momentum in the corporate space, where it was already very present, but the whole family of Linux was very well established in servers, firewalls (more BSD than Linux here), mobile devices, embedded hardware, etc
I’m not defending their overall argument, but I don’t think they are talking about the 2018 Red Hat acquisition, rather IBM’s 2000 announcement they were investing a billion dollars in Linux: https://www.cnet.com/tech/tech-industry/ibm-to-spend-1-billi...
IBM has been a big contributor to Linux long before buying Red Hat
But why do they do it in the first place, instead of investing in their own obviously supiriour massively invested in OS's? Because Linux IS better, and the whole idea of it is better than some closed source crap. By nature of the GPL license it will snowball and everyone else will be left behind.