I used to be IT and now I'm in sysadmin work. I don't make corporate software decisions personally but I work with the folks who do. You're not entirely wrong but you're being extremely reductive.

Browser decisions are less about complaints and more about minimizing the ability of third party vendors to blame issues with their sites and occasional business required extensions on our browser choice.

Vendors would be more likely to support Firefox if it was more popular with the public, but that's more of a second order thing than some arbitrary "avoid complaints" decision. Fuck, half of sysadmin is selling the business on whatever shitty change you have to force on them because you don't have a reasonable choice. Avoiding complaints is so far down the priority list that it's routinely ignored.

The move to Chrome from IE where I work was caused by the vendor providing our timecard site making changes so it would only work in Chrome. One could argue "just drop the timecard vendor" but that's a decision outside of IT's hands (timecard and payroll is HR's domain) and a change like that is too massive to kick off due to something like what web browser needs to be used. That effects payroll, time cards, employee reviews, taxes, access to benefits... too much to just go "IT says no"

For reference, this was ADP. I know not all of their contracts went through this (my wife's workplace uses ADP and somehow is still on IE, their lack of IT security scares me) but again, not for IT to negotiate. Best part was that we had other business critical sites that still required IE, so while Chrome was the default, we had people using both.

We've since changed to Edge as default as vendors were dragged kicking and screaming away from IE and activeX (shudder), but now we still keep Chrome around for the vendors trying to get out of fixing their shit. Avoiding complaints does come into it, but far less than you'd think.

As far as MS Office goes, yes familiarity to the office workers comes into it (employee efficiency and saving time on training trumps personal stands about open source). There's a lot more to it though. You can't call up GNU support when OpenOffice shits the bed, we can and do with Microsoft sometimes just to calm a VIP. Having someone external to blame for things users don't understand is a valuable tool. We can rely on MS Office having easy configuration options so we can meet the various regulatory requirements our company has. MS Office can be managed through the same tools we already use to manage OS settings in our environment with no custom work or additional software. We don't rely on sometimes janky open source reverse engineering to open document types we recieve from outside our company, risking formatting issues causing problems with legal documents (yes, incredibly unlikely, but why even open yourself to the risk).

Admittedly, my workplace is "full contact" Office use. The things these bastards get up to with functions and macros is amazing and horrifying. When I was on the helpdesk I lost track of how many times I had to walk high level people through the fact that no their machine was not underpowered, they did not need more RAM, but that they had hit the limit for data in a single sheet in Excel and the only solution was to work with smaller amounts of data at a time. Since I've moved to sysadmin I've lost track of how many times we've had issues escalated to us because some department has constructed a faux DB using a bunch of Excel workbooks and data connectors between them. Just happy I'm not our SQL guy trying to move them away from that, poor bastard.

Anyway, at any medium or larger companies, these decisions have a lot more going on than tech dude preference and trying to avoid complaints.