I personally think CoH was still doing well, just not as "well" as NCsoft would've liked. NCsoft saw an 8 year old game that had definitely peaked, the $$$ from CoH was only downhill from when they made the decision to shut down.
I believe it would've been a very long and slow downhill, but CoH had most likely peaked. NCsoft saw this as justification to get out. Also, NCsoft was probably looking at the ROI, return on investment factor. Because of CoH's age it had a lower ROI. So even though CoH was making money, it was making less than an investment in another property would.
Basically, NCsoft puts $1 into CoH, they get $2. They put $1 into GW2, they get $5. Translate that to millions and its a big difference.
NCsoft closing CoH doesn't make them stupid or malicious, its the way it was conducted that was wrong. If NCsoft didn't want CoH they should have:
-Ramped down development and slashed Paragon Studios to a smaller team.
-If that didn't work for them, go to "maintenance mode".
-Sell CoH to highest bidder.
The business side of shutting down CoH kind of makes sense, the Customer Service side however...yikes.