No you don't know if the OPs husband has always been disabled.
Yet you still assumed that he could have commuted further, worked harder, retrained more.
Generally though, all other things being equal, it's easier to work/retrain if you are childfree
All things aren't equal. The OPs DH is disabled.
It also ignores all sorts of other things that impact upward mobility.
People who come from areas of generational poverty find it harder to access better work and training opportunities than people from middle class/wealthier backgrounds for example. Generational wealth makes a difference. It can be harder if you are an immigrant for from a minority background.
So Im not sure how you have decided that not having children, one of several factors that can impact earning ability, is the great equaliser you can use to berate the OP for not overcoming any other difficulties you may be unaware of.