Because bikes are now marketed as toys for those with disposable income rather than as a cheap mode of transport for the masses, the marketing people at the oil companies know that these modern bike owners are prepared to pay a premium for oil rebadged as being specifically for bikes. If you're happy paying thirty odd quid for your oil, then fine, whatever makes you feel good. I will continue using car oil in my 160bhp ZRX and in all my other bikes.
As I said earlier I have to keep a barrel of bike specific oils for people whose bikes I work on who won't be persuaded that they are being conned. I paid fifty quid for 25l of Elf oil. Funny thing is these people who insist on having the bike specific oil also insist on paying a premium for it, so that barrel will be used up at thirty quid for each four litre refill. If I charged them any less they wouldn't be happy.
There exists some contested argument both lines....Read up on bike wet clutches and contaminant due to wear, read up on car dry clutches, read up slip agents, on friction and viscosity, engine materials and stress/fatigue
You'll actually find market forces at work rather than you sinister perception perhaps... The oil companies respond to demand, if all the 'modern bike owners' you refer to did not demand it, then we would all be sticking car oil in our engines... But we don't... Because we're not conned by proper riders who spend grands on a ZRX THEN scrimp on a few quid in proper oil.
Who cares..Carry on mate... You do what feels best for ya,
In fact let me help you...ALDI have an offer on, 5ltr car oil for £4.99 .... Hurry , but if you are going to ignore the labels on oil ... run your ZXR on their veg oil, a mouth watering 99p.
To show I'm only taking the piss a little... Here is something from the respected MCN you will enjoy...
http://www.nightrider.com/biketech/oiltest1.htm