Not tricking them into buying it, and not bethesda specifically. Tricking them into thinking it's in their best interests to buy it, when really it benefits the publishers more than anyone else.
It's the same reason supermarkets always have 'Buy 1 get 1 free' or '3 for $5' deals on, because they give people the impression that they're getting a deal and convince them to buy something they wouldn't have otherwise. 'Here's a way to get all our DLC for less!' is following the same strategy. They don't do it out of their love for their customers, they do it because they know it makes them more money.
If you were planning on buying all the DLC no matter, then you're still better off spending the extra $5-$10 to get them individually (assuming you're getting them as they release) to ensure that you're not wasting a larger amount of money on extra content that you don't enjoy, or doesn't live up to your expectations.
The only time I can see an arguable case being made for seasons passes is if you're picking them up after all of the DLC has already been released, because you know exactly what you're getting and you are indeed getting it at a discounted price.