] Why didn't W try to fulfill his own wishes by hard work instead of blaming Darcy and run away to the regiment?

We have to remember that the upper classes of JA's time had a very different attitude towards money than we do. They didn't really admire a "self-made" man - they'd simply be suspicious about how he managed to make so much money honestly. Yes, it was all right for a man to work for his living, but only in certain lines of work (if he was in business, it had to be a kind that required a considerable financial investment to begin with). It was much harder for a man who wanted to be considered a "gentleman" to go out and get the kind of job that would let him live by the standards of the gentry. Men as well as women expected to either inherit or marry their money, not make it themselves, and nobody looked down on them for it (unlike modern society). Also, "connections" were very important, as we see throughout P&P. You got ahead in life by who you knew, not so much by what you did. The Darcy family were Wickham's "connections", and as far as Elizabeth knows at this point, Mr. Darcy Junior has failed in his duty to help Wickham along in life.