My son and I replaced bad lifters in a 5.7 hemi and it is a sizable job. Heads have to come off along with all attached to them. All of the other issues you find should be addressed and you will find some issues. We found a number of broken manifold bolts that had to be replaced. We replaced all of the timing components, chain, sprockets, and phaser. We also discussed installing a high volume oil pump, but funds were running low so we disassembled the existing pump. It was found to be in good condition so we cleaned and assembled it. It was installed and provided good oil pressure.
As for why these failures are occurring, we discussed the possibility of low oil flow as the most likely reason. My son says that oil in modern engines is asked to do too much operation of internal hydraulic components. We both agreed that if we ever took on a job like that again, a high volume oil pump is a necessity, especially on engines that idle a lot. That is when the pump turns the slowest and can’t deliver enough oil at such low speeds. There may be enough pressure to keep the gauge off of zero, but you need flow to lubricate the upper end of the engine.