I would guess that the RC cars & planes / drones are mainly bought by 'younger' enthusiasts who are probably less worldly wise and have a now, now, now - must buy/have compulsion.
Most boaters that I have met are more 'mature' and so are happy to wait things out and to look for a proper price rather than just throw money at things.
Also, I look at some battleships that are absolutely covered in fittings - guns, railings, bollards, hatches, lifeboats, radars, winches, cranes, aircraft, etc. and then you see sellers wanting £5 each and upwards for those fittings and you quickly do the maths - it adds up to be crazy expensive to get the ship on the water unless you search out bargains or learn to make your own fittings.
Railway modellers seem to be different - almost everything in their layouts is off the shelf - they seem to just accept the constant emptying of their wallets.