I'm sure that it works and I understand it's in poor taste to cut down a system that someone invested in and enjoys. When you say there is no reason not to, I don't really agree. I don't mean to derail this thread too far but here's just a brief list:
Internal element:
Pros: less heat loss in the system, does not require recirculation during heating, more compact system, same heat source for mash maintain and boiling, less chance of scorching, ability to clean (physically with a scrub pad or brush) the element in place without removing, less complicated, more compact system, cheaper.
Cons: Requires a false bottom for BIAB or a rigid basket to keep grains away.
RIMS tube:
Pros: Does not require a false bottom... having trouble finding more here.
Cons: More expensive, more complex, requires a pump, requires pump to be running during heating, higher chance of scorching if grain compaction happens or if pump speed exceeds drainage, element must be removed for inspection, boiler requires a separate heat source for boiling.
Again, I'm not saying it doesn't work. I'm just saying it's not the best choice and that's coming from someone who sells RIMS tubes and stands to make more profit when someone buys it.