So how many of those other major sports can have their playoff games ruined by teams not in the playoffs?
That's a fair point, but it's the price you pay, when 'playoffs' can't be separated into 'brackets' like other sports can. No ones going to watch a 10 car race, no one wants to watch a bunch of 1 v 1 races either. No one will watch the end of a season, if a front runner has too big of a points lead.
Basically, NASCAR has already conceded that their season is too long. They knew that by the 26th race, people were losing interest. So they created the chase, to shake things up, and start fresh, and make it interesting as if the season was re-beginning. Instead they should have just shortened the season.
On the other hand, it's a business decision. How many viewers do you think NASCAR loses because of length? Now how many would they gain if they shortened it? If they can't gain more viewers than they lose by dropping 10 races, it doesn't financially compute.
http://aol.sportingnews.com/nascar/story/2012-11-21/nascar-tv-ratings-decline-fox-espn-tnt-daytona-500-olympics
Coverage on Fox, TNT and ESPN averaged a 3.6 Nielsen rating and 5.8 million viewers through 35 of 36 races (not including Sunday's season-ending race at Homestead)
So, 5.8M per race.
If NASCAR cuts 10 races, they lose 58M 'views'. (Non unique)
That leaves 26 races, to cover that loss. 58/26=2.23
Meaning, that NASCAR would have to hope they gain 2.23 million
new viewers PER RACE, to acquire the same amount of
total views in their existing 36 race season.
That's not even accounting for the loss of 300 hours of advertising from the 10 races cut, which would have to be covered by an increase in per-ad-price during the 26 season race, which they couldn't do, until viewership increased enough, to justify the increased cost per add.
Still, not accounting for the contracts they have between Fox/TNT/Speed/??? to broadcast the shows, and the money they make from them.
Tl:dr
From a business standpoint, NASCAR doesn't care about the viewers, and would make more money, with less viewers over more races, than versa visa.