I like big chests and I can not lie.

Leave the whatever 10% chance on beating a boss for the first time in a reset to drop a chest the same, but add something like, if a boss did not already drop a chest, every subsequent kill has a 2% chance? 1%? to drop a chest until one is dropped.

Chests serve an important function in the game. Especially early resets, they can help get players over whatever walls exist for them and try to get some more gear. But we get only one chance, purely luck. if you have terrible luck, the run may feel unsatisfying.

Really feel stuck? Go back to the previous one or two bosses, leave the game a while, collect xp and a chest, get past the hump. This still caps the maximum number of chests per game. This is still not the best way for high idol count players to speed through and get chests since enemies spawn at a certain rate. But especially if you feel like you've been unlucky with gear or are hitting a lot of walls, you can hope for a couple more chests in that run.
Also you can't just leave the game and come back to 2000 chests. You'll come back to 1 chest.
It also means people will probably feel more in control when saving up for a campaign challenge because they can decide that they are saving up not just waiting for the game to allow them to save up and do a challenge.