Here's my long-winded upgrade motivation saga...
I was pretty slow to adopt most new trends in mtb after about 2007, as I spent a really long time on/off in college/Uni, which I didn't start until I was 27. By the time I finally reached my education goals and found a career, I was in my mid 30's and still flat broke. From 2009 - 2016, I pretty much relied on hand-me-down frames or whatever was super affordable, and whatever parts I could muster up through friends/connections/buy'n'sell. It definitely helped launch my renaissance when I did a few Co-op terms at Rocky near the end of my schooling (cheap deals, a free used frame, etc), but after such a long time in school, it took a long time to be able to afford new things once out the other side.
When I had squeezed everything out of my free '14 Altitude Alum frame, I found a nice compromise with the '15 Giant Trance, after really liking the one I had found for my GF a couple years prior. It seemed like they could be found everywhere for cheap, and although they weren't quite burly enough for Shore/Sea2Sky (IMO), I only broke one chainstay in 4 years of riding it (crash replacement). In the last year of riding the Giant, I focused on increasing my quiver, as I wanted to replace my unrideable 2007 Norco DH, and my '13 Aperture hard tail. Neither of those bikes got ridden anymore, because the Altitude and Giant had better fit/geo/wheel-size, and now I was spoiled (foreshadowing).
So I compromised a bit on the 2 auxiliary bikes. I got my buddy to make me a hard tail, with the general Geo/purpose I was looking for (no compromise), and I found a brand new 26" Aurum frame that I could use as mullet with a 27.5 fork, that was really cheap old stock an NS Bikes but still had a full warranty (compromise). Great, now I have a wicked hard tail, and a bike that didn't break the bank for the dozen or so shuttle/park days per year, which saves my trail suspension bike from severe beat-downs.
Last year was the straw that broke the cheap-guy's back, and everything seemed to line up. The Trance was getting clapped, and risking another crash replacement. Geo had evolved lots over the previous few years (HA/reach/SA), my hardtail had me loving more reach and steeper SA, and it was trickling down to more affordable complete bikes. I was finally at a point financially where I could consider selling some old stuff and buying a complete bike. I turned 40 in early February (B-Day present), and it was time for my first new complete trail bike since 2004. My budget oriented self landed on a Ripmo AF, knowing the important aspects for me were better geo, a frame that fit, and suspension I could tune and work on (also my first 29er). I was satisfied that any additional parts upgrades could be done over time, and the fact that I had it before the Covid Boom was just icing on the cake.
After that, it's been a few upgrades. New brakes for the Ibis, which made the brakes on my other two bikes feel hopelessly inadequate. That led to new brakes on the other two. Tannus inserts in the hard tail, and now I'll be looking for some for the Ibis once the season gets rolling. Slippery slope, that upgrading.
TLDR: As soon as I reached a point in my life that I could afford upgrades for the sake of upgrades, it all starts with one bike/component. Then the others need it. After typing all this out, I understand why many are saying "don't demo bikes regularly unless you want to buy". This also makes me understand the appeal of one do-it-all bike, but I guess that's just one compromise I'm not willing to make. Upgrades can be a slippery slope with no end, if you don't find a reason to control the slide.