Toby died of cancer. Which was inoperable by the time it was found. It had spred to far and to fast.

Tom's passing was due to several problems. Possibly early mild stroke that went undiagnosed, congestive heart failure, hypertension, and chronic arthritis.
Don't sound like much or that bad. Until you get into the medicines to treat the problems.
They couldn't treat any of the problems without messing with or causing problems some where else.
The arthrtist itself usually leads to being bed fast.