I can't speak for others. But for me, using Zoom is really because it worked better than everything else I'd tried (Skype, Google Hangouts, WebEx, rolling my own SIP server). That was parts: Linux software reliability (WebEx, Skype), limits on the number of people that could join meetings (Hangouts), and effort to talk my collaborators into installing new software (SIP+Jitsi). A bonus is that my employer had an institutional Zoom account. I've been happily using Zoom for 2-3 years now. I'm unhappy about these privacy issues that are being discovered/discussed now and I kinda feel like I should have looked into it. I'm sure there is a bandwagon effect happening, but there was also a real component of it working better than other solutions.