Petey said it got worse and worse which is consistent with how Dr. Google says about the injury. I think it's reasonable for those of us who play sports at a (much) lower level to take a see how it goes approach to nagging injuries. Especially when we're teenagers. Who wants to go see a doctor or go for rehab? But Petey is a professional athlete who should know that his injury was different and was impacting his game on the ice. With free and easy access to team doctors and treatment specialists, I would assume he wouldn't ignore his knee tendinitis for long especially since it became worse and worse.
I think you're assuming too many things here and trying to lay blame where maybe it's not necessarily warranted. I've played through some pretty serious (abductor / high ankle sprain) injuries when I was in university. I spent 2 - 4 hours a day for months on end getting ultra sound massage, ice baths, heat therapy, wrapping, stretching, exercise, ect..
All in an effort to get me ready to go every weekend, which I could albeit with some definite difficulty. We had a new coach from overseas and as a 4th year player they just wanted me to play no matter what. Now, obviously pro players with 8 year 11.6 mil dollar contracts should be treated better/different but I can absolutely see the team and Petey trying to navigate through an incredible (and important) season to keep him on the ice. Especially with what seems to be a a non career threatening situation and a definite lack of suitable replacements.
A simple google search gives the following:
If a person has mild tendonitis, they may be able to return to their normal activities in 3 weeks. In more severe cases, it may take 3 months or more to recover.
Now if it were to be a 3 month recovery I can see why they didn't shut him down as we didn't have the luxury of having a replacement capable of keeping our perch at the top of the division/playoffs.
It's pretty easy to make judgements in hindsight but I think he probably deserves some credit for fighting through a lot of pain and loss of mobility. He's shown to be a fantastic player and he probably deserves some leeway, appreciation, trust, and understanding.