Cranking issue

My wife was driving the car and she said dash lights started popping on and before she could do anything, the engine shut off.
I went to see what was going on. Car engine would spin but not crank. I suspected possibly the starter and towed it home.
When I got it hone I noticed the water pump serpentine belt had broken.
At that point I suspected possible timing chain issues as the engine has 240,000 miles but runs like brand new. Always PM all my vehicles with the best oil and parts I can buy. Mobil One Oil and Mobil One Filter.
I tore the engine down and found that the timing chains (3) were all intact. Nothing broken and chains were really not that bad. Premium quality!
Having done the tear down I figured it was a great time to replace the timing with a complete new set of chains, gears, tensioners, etc. Had all the timing marks as per stated. (I own the Shop service manual) and followed instructions to the tee double checking everything. I know I have that all right as I have turned wrenches for over 50 years.
I put everything back together using new gaskets, belts, water pump, new starter etc, nothing short changed!
After completing the repair I go to start the engine and nothing changed, still spinning but not cranking.
My question: The serpentine belt broke (it has 2). The one that broke is the water pump. I can't see how there could be any valve damage as it has timing chains which were not broken. Do you think it overheated and wasted the heads and head gaskets? I can't think of anything else it could be. Interference or non-interference engine plays no part here as it has timing chains and therefore a serpentine belt issue should not bend valves.