I get this with my brother too.
Every time I visit him, which isn't that often, just a few times a year, I am asked to fix his bike. Every time he has "another bike." He cycles about 10 miles a day to work and back on a BSO. Every time I visit him, his wheel bearings and BB bearings nd cones are serverely worn. I stripped a wheel down once and showed him all the sparkly stuff in the bearings. "Thats metal that is," I told him. I showed him where it was coming from and told him that it also accelerates the wear rate of his bearings. I told him that the bike I used to get myself to his house, about 100 miles away, cost me £250 second hand, has done at least 50,000 miles, was over 10 years old, has had about £300 worth of replacement parts, some of which are still going strong, is still working very well and will last for much longer. Then I ask him how many "cheap" bikes he's bought in the last few years and ask him how much they all cost. I then ask him if he want me to build him bike that will last for about 10 years and need hardly any maintenance and have as low a running cost as possible (he'll never bang the miles out like I do so that wouldn't be too difficult)
He's just unwilling to spend the money on what I assume he thinks is,"just a bike." I know that he has the money but he just won't spend it on a bike, which he needs to get to work.
I refuse to help him now. He asked for my help and I've tol him what to do. It's up to him to help himself now. I'll help him pick a bike, but I won't bother repairing his worn out tat. Or I might just treat him to a decent bike if I see a good bargain.
I've nothing against BSOs. If I never had a stock of old bike bits that are close to their end, I would have one myself for popping to the shops and leaving out of sight. But I have a knackered old fixer for that, which gives a much better ride than a BSO.