Any company would never know the benefit of marketing in the Bitcointalk community unless they have tried it at least for once. I wont blame them, they don't trust their instincts when it comes to marketing their products. If not for anything the entire companies that has run their marketing in the forum are not stupid, if they don't see the benefit they wont do it in the first place.
$500 per month budget is too small. Did you give them a response or you just ignore the conversation?
What I believe is also a reason why hardware wallet companies are not eager to advertise their products in this forum or aren't ready to spend a lot of money on it is that they are pretty much receiving free advertisement thanks to Bitcoin and its adoption. Anywhere on the internet, including this forum, when a newbie asks what wallet they should use to store their Bitcoin safely, most people would tell them to use hardware wallets and suggest a few names, which usually have Ledger or Trezor in them. Even if they aren't given names, once people say they should buy hardware wallets, they search for them and will probably reach the ones primarily used and suggested in articles, blogs, etc.
Most of us promote their services and products without getting paid, and they probably know this. This might not be why they are not interested in promoting themselves here, but I'm just saying they are already getting promoted without spending money on it.