To get the free oil change I'd have to take time off work so I could spend 3+ hours or so in total driving to the dealer and waiting around for it or try and do it on a Saturday which will spoil my Saturday and it'll likely be busier and take even longer.
I also have to nag them not to wash it which they end up doing half the time anyway, which creates water spots on the way home as it dries. And don't get me started on the nasty goop they spread on the tires.
I also really try to avoid "other people" working on my cars, although to be fair my dealer has usually been fairly competent in the past.
Yes, I'm anal.
Ordered the kit from ECS, picked a nice day, and was done in under an hour for $60. Cheaper than taking time off work. And some quality time lying underneath the car exploring.