(conversely my current desktop boots so fast that I now shut it down every day. Saves a bit of power, and a clean start to each day feels good.)
But it's important to understand that back in the 90s running a machine for long periods was unusual. 18 months is certainly notable. Of course there were no security patches back then (and largely no need for them because the always-on Internet wouldn't happen for another few years.)
It's hard to understate just how unreliable tech was in the 20th century. Cars broke down a lot. Computers needed rebooting all the time. The risks taken during Mercury, Gemini and Apollo would be considered completely reckless now.
It has ever been thus. In the first world war more pilots died from mechanical failure than from enemy fire.
First we make it. Then we make it fast. Then we make it reliable.
You should try Windows. After some days it becomes confused, some things (especially USB stuff) will not be recognized, programs will not load correctly etc. It is an old bug ( i've seen it also in Win 7) and nobody at Microsoft seems to care about it. Of course, a reboot fixes everything.
On the server, especially when running in a VM, Windows can achieve impressive uptime, I've seen one NT 4.0 server with over 5 years without a reboot.
These days, the question is if you want to keep a server up for that long just because you can. When I worked as a Windows admin, I usually rebooted the servers after installing updates.
I haven't had the experience you're describing since everything moved over to NT. I.e., Win95/98 did that for me, NT4, Win2000, XP, etc have never exhibited that behaviour for me.
I think this take, as a generalization, is a couple decades out of date.
.... Really? Ignoring the "nothing should have that uptime due to security patches" best practice, almost everything should be able to do that barring power or hardware failure.
My OpenIndiana NAS has done >1 year uptime two or three times now. My OpnSense firewall did once (too much road warrioring for a period) but could do it easily again. Linux VMs have done that many times for me when I've been lazy on patching or too busy My ESXi hosts do that too. Thats just my basement homelab, nothing special.
I installed a cluster of Windows 2003 servers in a customer site a looong time ago that did over 1000 days uptime (no internet access/customer didn't patch/etc).
I even had a Windows XP laptop in my garage 10+ years ago that did nothing but Chrome and RDP client go over 400 days before I tripped on the power cord.
Yes, systems should be patched and all that. But really, anything not forcing updates should be able to do a year.