Sure there's a reason. So that they can make more money off you by selling you another course later.
Why? You think there should be some sort of SCUBA 'hardship' fund?
PADI developed a
model for scuba tuition that was
modular. They break the training into various levels and elements. As I've said before, the OW course is the
entry-level course. There are other courses following that, which can be selected by the individual diver according to their needs. That system actually
saves your money because you only do the training that is relevant for your needs.
People can be a bit idiotic to think that breaking those courses into modular elements is some sort of rip-off. Dive shops charge for their courses based on the cost involved to run them. This is usually broken down as:
1) Cost element for materials - Manuals, tables etc.
2) Cost element for equipment - SCUBA gear depreciation, cylinder filling, compressor maintenance etc.
3) Cost element for Utilities - Water, Gas, Electricity for shop, pool heating etc.
4) Cost element for boat operations - gasoline, maintenance, depreciation.
5) Cost element for wages - instructor, dm, captain etc salaries/commission
These cost elements are normally distributed, to provide a cost
per dive. Thus, the major calculation in pricing any given course is
the number of dives it contains.
So... a 4x Dive 'Entry-Level' OW Course might cost $400
a 4x Dive Rescue Course might cost $400
Total Cost for SCUBA and Rescue skills is $800
A 'comprehensive' OW Course, with Rescue skills, would still have 8 dives. So it would still cost $800.
The same.