Toulon A milkshake too thick or too thin is not a milkshake!
I think most fast food places serve them too thick because it takes very little time for them to melt to a consistency so they can go through a large straw. They don't want them melting too quickly. I stop by Wendy's drive thru a lot and get my wife a Frosty. It takes me 5 minutes to get home. Usually just before I get home it has thawed enough to go through the straw (I have to sample it to make sure it is suitable for human consumption).
As a kid before shopping centers and fast food my mother would take me downtown Christmas shopping and we would have lunch at a Walgreens pharm that had a grill. My big treat would be a hamburger,fries and a hand made chocolate malt. That was the best malt. A milkshake can't touch that.