I can speak only for myself, but the one thing I hate the most about opening a BL Chest is getting something that I can easily get just by playing the game. This post is focusing specifically on the guaranteed drop. The value of that drop, in my view, is what drives me to either open a chest or hoard keys until the next version is released, hoping for something better.
Some negative examples:
Halloween 2018 drop: https://wiki.guildwars2.com/wiki/The_Evon_Gnashblade_Trick-or-Treat_Bag
Seriously? I was getting 200-300 bags an hour farming the lab, and they had the same contents.
Zephyrite Festival 2018 drop: https://wiki.guildwars2.com/wiki/Gnashblade_Zephyrite_Supply_Box
I watched many youtube vids of people opening tons of BL chests, but these bags were also easily obtainable by trading in material to the zephyrite vendors.
Gandarran Stronghold 2018 drop: https://wiki.guildwars2.com/wiki/Black_Lion_Lockbreaker_Kit
This was painful tbh. If you spend any time at all in HoT maps/metas or in Dry Top / Silverwastes, you have these items by the pound.
Distant Visitors 2018 drop: https://wiki.guildwars2.com/wiki/Black_Lion_Material_Bag:_Istan
Crafting materials. Just plain old crafting materials you can find by killing neutral wild life, or opening heavy loot bags in WvW.
Some positive examples:
Armored Assault Chest 2018 drop: https://wiki.guildwars2.com/wiki/Mini_Baby_Mount_Container
Who doesn't like minis? Rather than buying them with statuettes you got them here. Already have it? You can craft the next colour version or sell it on the TP.
Mysterious Etchings Chest 2018 drop: https://wiki.guildwars2.com/wiki/Black_Lion_Chest/historical#Guaranteed_drops_7
See comment right above.
Now let's turn and look at the current guaranteed drop, the Battle hardened chest. It's contents? Food items you can purchase from the provision vendor, potions of WvW/PvP XP which you can earn by completing the dailies in either game mode, and grey vendor items worth 1g or less. Hardly compelling.
Full disclosure, I already have the Wild Magic Backpack and the Kings throne doesn't appeal to me, so I have little interest in this chest anyways; but the reason I have a bunch of keys in my bank in the first place is because after opening a few of the halloween versions, I realized I was getting stiffed on the guaranteed drop because I was farming hundreds of those bags per day already.
Now I'll hold onto my keys until the next chest.
I realize that most people are opening chests hoping for the uncommon drops. I'm more of a realist, and while I like the thrill of maybe getting something awesome, I'm more focused on the two items I know I will get for my key. While doing a weekly key run is hardly onerous, you can only get 1 per week, which in my view makes a key valuable. Same goes for spending gold or real money to purchase keys. So when I open a BL chest, I want to know that I will be getting something that I cannot get just by randomly killing a mob or completing an event.
None of the Common Drops can be acquired as random loot in game (except those Heavy Crafting bags - those need to go too), so neither should the guaranteed drop be either.
MY SUGGESTION: Please insure that future guaranteed items offer rewards that can only be obtained from a BL chest, so at least we feel like we get value from using a key, even if we didn't get a Permanent Hair Stylist Contract.
TLDR: If BL Keys are special, the contents of the BL chests should be equally special. If the potential rewards are grey vendor trash or random crafting items, why bother going through the work and expense of acquiring the keys in the first place.