COST
not everyone can afford a 6-8K quad
its simple
The other 2 strokes that were out in the 80's were crazy fast, dangerous and cost a lot.
Kids were getting hurt on these big bikes and law suits were being thrown at Honda, Suzuki and Kawasaki etc .. it cost us all the the great 3 wheelers of the era and the 250R quads.
Yamaha saw a market for a low cost ATV, simple in design as an entry level machine. For performance they had the Banshee. Something that was easy for beginner riders and still fun for more experianced riders. Cost was a big issue to snatch up the market. Yamaha used 3 engines to develop 1 that way they could produce a lightweight, lowcost engine without re-tooling and spending millions on a new engine production line.
Thats what made the Blaster one of the best selling Yamaha ATVs of all time.
Thats why the chinese bike/atv market has gone through the roof. now anyone can afford a bike, hell for the cost of one raptor and antire family of 4 can each have their own machine... the ones that were looking for brand name machines had the Blaster.