An Uncanny Coincidence?

Just recently had some repair work done on a 2000 Chrysler T&C minivan - 70K
miles
The oil pick-up tube was clogged with "debris", the shop guy hesitated to
say WHAT it was.
I have changed the oil every 3000 miles up to 50K miles and since then, I
have let it go to 4,000 miles maybe twice, and 4,500 once, using Castrol GTX
and always changing the oil filter.

After getting the vehicle back, my wife drove through some standing water
about five blocks from our house and immediately lost power steering
capability and the temperature gauge was overheated when she pulled into the
driveway.
Well, of course the serpentine belt came off the pulleys.

Can anyone tell me WHY and HOW such debris build up could happen, and does
the serpentine belt need to be removed/loosened to remove the oil pan and
reinstall it?

Thanks for any info.