[DJ123]

Many don't these days (unless you're buying it) due to the costs behind it. Which is why big dealers have specific test ride bikes to take the cost/depreciation hits.

Bike has to be cleaned and re-inspected after return
wear and tear on components (someone may abuse it tyres/chain/brakes etc)
mileage updated on advert/diminishing the service interval
more miles on bike (depreciation - how many test rides do you offer?)

At the end of the day what does a 30 minute test ride do, except tell you the bike is different to what you have? You can't get to know how it really rides, performs and copes with everything all in 30 minutes.