I don't quite get what you're trying to say. I said that championship quality D1 teams probably won't be able to make any significant profits, which I am sure you agree with. I also said that teams that still make the playoffs can make high profits. The numbers you posted seem to support my statement.
An average payroll for a competitive D1 is between 500k and 600k
This is true. When I was in D1 some playoff teams had salaries in this neighbourhood. But I also remember that the average weekly revenue in Canada D1 was $760K. A competitive team with a 500k payroll would make $260k/week which would be over $3 million a season. By your own number a "competitive" D1 team could make $10 million in 3 seasons
And you should also ask yourself if you think you would be able to make anywhere close to $9-$10 millions in 3 seasons, as some people who tanked have admitted to, but without tanking (or being at or below the salary floor).
Anyways, you can still field a competitive team at the salary floor and make much more than $10million in 3 seasons. You just need to find viable D1 starters with low salaries. The new FA rules, however, make it harder to do it, since most of these kind of players would have salaries above $60k, so you can't acquire them from Free Agency anymore.
Besides, you should just ask yourself why would anyone tank in any division, even lower divisions (where there are human managers that is), instead of "doing well" with a middle of the pack or a good team if the these were the more profitable options...
Remember tanking is boring, but it is easy. All you need to do is login once a month. The other more profitable options involve alot more effort, like scanning the transfer list for good players, setting your lineup and replacing your aging players with younger ones. Managers may not have the interest or time to do this, so they opt for tanking.