When the range rover's headlight breaks and a used part is about 100 quid, vs the same thing happening to the defender, and 10 quid from a breakers.
Or one of the hundreds of sensors, or ECUs goes tits up on the range rover.
Or the wing mirror gets knocked off and it costs a fortune for a new one.
Or it needs a small job doing and you have to pay a garage to do it, just so they can reset the computer with their gadget.
A 10 grand defender will last you year after year, and when things do go wrong they'll be a fair bit cheaper to fix.
A 10 grand range rover will go wrong year after year, and when things don't go wrong for a little while, you'll be saving up for when they inevitably do.