I still have a Trek MTB I bought new in 2000. In excellent condition, not a scratch on it, and great for popping off out to the local shop for something.
However my 4 new bikes are a result of my rekindling my passion for cycling and getting back into the sport a year ago. I'd sold my last previous road bike, a Cannondale from 1998 a decade ago and never replaced it when I emigrated to the UK. A 17 year stint there that saw me nearly abandon cycling altogether due to my being a wuss, mainly. Hated the cold, dark days and miserable weather combined with long work hours. Just stagnated. Happily, my move to Portugal 2 years ago has been great for many reasons, not least cycling.
I don't like to pay RRP so got a good discount on my 2019 KTM e-MTB (now my wife's preferred bike) and my 2019 KTM Scarp Sonic 29er MTB that I race. My 2019 Wilier Zero.6 I got a 55% discount in a sale - the last two eventually sold for only a 20% discount so I was lucky. The 2020 Trek Madone SLR I collect next week I'm also getting a reasonable deal on. I expect these bikes to last awhile.
The e-MTB will last until it falls apart, which will be decades. The 29er I race and will last until I break it. The Wilier is my climbing bike, I really like it and at 6.1kg, is future-proofed for weight and I can drop that to 5.5kg or less with a few upgrades if I was inclined to do so. Finally, the new Trek will get upgraded next year - groupset and wheels - but will be around for some time I think. The upgrades are to go electronic and lower weight since I will be racing it.