What is wrong with loyalty? When we buy a particular brand or product and have had nothing but good to say about it we tend to stay with it, and if we've gone with that brand for some time we continue to buy it even if it's no longer any good or doesn't last as long as it used too. What it boils down to is habits.
I've been a Chevy truck fan ever since I could drive. My dad got me started on that and I have not stopped yet! I always bought Chevy because I know how to work on them, and buying another make of truck would mean having to learn how to work on it, and that takes a large amount of time, time that could be spent doing other things. Another reason I buy Chevy would be pure habit, http://ergonomics.about.com/od/ergonomicbasics/f/what_is_a_habit.htm . A habit that, for me, is very hard to break. Just like some people vote for democrats simply because they have always voted democrat, and their parents before them voted democrat. It's become a habit that's so ingrained that you don't even notice your doing it. Habits can be good for you, they will keep you going down the right road, keep you healthy, help you attain your goals.
Of course those habits can be bad for you as well; and bad for your wallet too. I once bought a lemon and kept it even though the thing was costing me a fortune just to keep it running, I knew I should have got rid of it but I was stubborn and went through the headache of keeping it going. This kind of behavior goes way beyond loyalty and into the realm of The Really Bad Habit. And we keep returning there as well, http://www.scientificamerican.com/article.cfm?id=why-we-return-to-bad-habits.
As far as my habit of buying only one type of vehicle I can honestly say that I see no wrong in this. To me it can be a sign of loyalty to Chevy and a loyalty to me in that I am content with following my "lovemark" through to the end!