Perhaps they think that by forcing everyone to go through the sales dept just to get the basic docs, they'll get better sales opportunities.

How do you upsell a hardware engineer who just wants to buy a specific chip, and already has everything to evaluate and use it? You don't. So you force everyone to go through sales, and then sales wants to talk to non-engineering higher-ups, and then the upsell happens - while the people who actually knew what they wanted remain as far away as possible.

And if you don't have the pockets deep enough for the sales dept to acknowledge your existence, then you might as well not exist.