Your math is not wrong. Part of the issue is that on the off chance that a team doesn't get that second run, or something goes wrong to where they can't afford their monthly payments, the Indebted runner is hosed. Also, while your math isn't wrong, it's not always the standard. Many GMs like the runners to be a bit hungry. This leads them tortaking more risks, which explains why they are running in the first place. This is more common with newbish runners. Additionally, there are GMs that encourage their players to diversify their skills, much like those skill choices used in Life Modules. In these games, the players will likely be going up against opponents with dice pools closer to 8 - 10. Finally, we come to the actual math-related reason: your character is losing 11000 a month. That money could be spent on new gear, medical bills, or anything else. But it can't, for the next 10 months. So for 20ish runs, you'll be paying off that one-time loan.
As always, the danger of a quality depends on the table. And any negative quality that does not negatively affect a character should not be allowed.