Timing belt what keeps throwing timing belt off why is oil black

Why do you think its off, , eyes on marks? or strobe light or? what?
old oil turns black , on purpose. so it dont fill the engine full of gunk.
dont run oil for 5k miles. 3k on high mileage engines. max.

the belt can fail because >
1: over 60kmiles?
2: not a gate belt but in fact a fleabay-china $5 belt.
3: cam cog bent.
4: someone set the tension wrong, (top cause , RTM)
5:oil leaks to belt , belt dies early death.
6: running no cover, or cover is cut to ribbons, letting sand and gravel kill the belt in short order
7: spraying belt with belt dressing, bad to the bone that.
8:: im sure there are are other ways to kill it early, but i give up.
9: oops one more , the last joker, failed to put the head to block guide pins back, now the 2 cogs are misaligned, and belt dies. early.

seem all ways, ask me...
what engine, there are many used, over the world on RAV4.

my guess
2.0 L 3S-FE I4 (petrol)
2.0 L 3S-GE I4 (petrol)