I'd say it was injuries that cost him his job, especially Moses'. After ten years without a premiership there needs to be a scapegoat, and any misfortune will be blamed on the coach. As you say, it happens everywhere eventually. The Tigers keep letting go of coaches and don't improve. Cleary and Maguire have both won premierships since leaving Wests so it wasn't the coach, but someone has to be the scapegoat. The coach is the only club official most fans ever see.
Timing kept him in a job for much longer then deserved
2014 epic fail missing the 8. That squad was a top 8 squad and Hayne reached his peak. Only had to win 1 of last 2 games against weak sides and copped thrashings.
2015 he got the Hayne Excuse
2016 salary cap ( Fair enough I pay that)
2022 - Strong sides had injury crisis and we got lucky. 8th best points differential shows where we were in reality.
Let's just say what we thought was BAD LUCK for Parra was actually good luck for BA.
One thing he was good at was judge of character. Lomax,Foran,Matterson,Lane yep he sure knew how to pick them.