Megas XLR didn't deserve to be classified as a tax write off.

Cartoon Network basically told the IRS that it was a gigantic financial disaster which let them subtract its production costs from their taxes that year (or something to that effect)

Because of this, if Cartoon Network revives the IP they would be forced to pay those taxes to the IRS. For obvious reasons, they won't ever do that for a 15 year old largely forgotten show that already considered a failure during its peak.

This was done without the consent or input of the actual creators, since CN owned the rights as part of their publishing deal. The creators have wanted to revive the series for over a decade now but haven't had any luck persuading the stuffed suits at CN to eat the cost instead of using that money to bankroll several new IPs.