Yes because that is the thing any sensible business owners would do.
Because reasons.
I love people who just randomly claim things like you can't see how much money the club has, or they'll milk the club for money, or random other things.
Every club publishes very detailed accounts showing precisely how much profit/loss they are making. We can see how profitable Utd are and that profit as Nicktay said, is incredibly related to on field success.
The Glazers have been in charge for ages and could have taken probably 100's of millions out of the club, they haven't. If they hadn't been successful winning titles and challenging for titles they wouldn't have been able to sign the latest sponsorship deals as. Well the difference between the deals top four teams are signing and even 6th place is phenomenal. Utd are making 100mil a year from shirt deals and sponsorship(just shirt, excluding the ridiculous amount of weird tie ins Utd has). Everton Newcastle are in the ballpark of 10mil a year, multiple teams are making 2-5mil a year towards the bottom of the table.
The money and profit comes from success, not killing the brand. LIkewise those other dozens of sponsors Utd have add even more income, the kinds of deals the sponsors aren't even interested in smaller clubs for.
It's rather like the Newcastle rubbish, fans insisting he's milking the club of money despite the profits being freely available on the club books, that they've made losses in more seasons than they've made profits, and that every penny from sales has been reinvested. They sold Cabaye late in the window and made offers for replacements but the deals couldn't get done, so he's obviously just taking that 20mil for himself....6 months of that bull then we see Newcastle reinvest that money in the next window, with their biggest buy being the guy they made an offer for in January.
They didn't buy big last summer because they brought in 5-6 players in the January window right before it.
The Glazers can make higher profits and have a more global brand(which helps other businesses as well) when Utd are successful.