I am half of a mature couple, we had two homes which we sold when we got together and we jointly purchased a 4 (doubles) bedroomed house with a massive garden thanks.......and you think it's selfish?
In our case, well we have adult kids/grandkids who live far away and need room to stay when they visit.
We both work from home.
And then we have elderly parents and we have room for them to come live with us if that is the best option. It gives us scope to remodel with all sorts of permutations depending on what unfolds. Maybe change a reception room into a downstairs bedroom with ensuite or maybe a room adjoining their bedroom into a sitting room to give them some independence. Maybe we or they will need a carer.
If we get strapped for cash we can rent rooms out.
Our eldest granddaughter has jokingly earmarked our loft conversion for her University pad
And then, there is the investment perspective, a house is a pretty good return over the years and we are building an inheritance for our kids to help them when we are gone.
I don't think any of the above is selfish, its a pragmatic response to our situation. We didn't deny any body anything, it was on the open market, anyone was free to make an offer. Does it matter if they are young or old, they had their reasons. And quite frankly its none of your business, you sound jealous and we have it because we can - end of!