I think the reasons why you were boarded are well covered by previous posters. It is a prudent thing to do.
As for service on the ground, at my carrier we do water services in these situations, it's just good customer service. Offering a full service is not impossible but can be challenging due to needing to guard the doors and then there is the need to be ready to go at a moments notice. But again, it does happen at my carrier from time to time.
For a route of the that length (3 hours), refreshment vouchers should be handed out if in the terminal. If onboard, a complimentary drink and/or snack is warranted. Two hours delay is the threshold for shorter routes. Again, at my carrier though, the senior crew are empowered to offer complimentary service, if they believe it to be warranted, on delays shorter than those. And yes, it's an LCC.