Im wondering why they didnt just put in the rule book if you have the vehicle trait you cant have war gear instead of putting it on each of the cards?

Well, two reasons, I'd guess:

1) Traits are not supposed to have any inherent rules in and of themselves. They are just ways for cards to interact with each other. Making it so that all vehicles automatically can't have war gear attachments turns "vehicle" into a keyword rather than a trait.

2) They may also be trying to leave the design space open. It's not completely impossible that a future battle suit unit, for example, would be heavy-duty enough to be considered a vehicle, but also allow for the use of separate, independent war gear.

Ok

I also didn't realize that about traits and keywords

Thanks

Yeah I'd say 2. Design Space should be as clear as possible. No need to limit everything when you can just have a small text clause on individual cards.

I'd bet a Riptide suit would count as a vehicle that could have some gear. I was a little confused that the Ultramarines Dreadnought didn't allow wargear but the Crisis Suit does. Interesting...

In 40k Dreadnoughts are considered vehicles while crisis suits are considered jet pack units. That's probably why they did it that way. A riptide would make a fair amount of sense though, even though its considered a Monstrous Creature in 40k rather than a vehicle.