It's mostly business spend. From what I understand, if you're charging six figures a month on a card (which is plausible for a decent-size e-commerce business: online advertising and shipping are basically always on a card), the Amex ecosystem is basically the only game in town. Chase et al tend to shut down Ink accounts that cycle (spend up to the limit and pay it off multiple times in a statement period) while Amex is exceedingly tolerant of that sort of thing. At that level of volume, most of your spending isn't viable for cash back cards with 5 figure limits, so the choice becomes BizPlats vs. BizGolds vs. DL BizReserves (there's not much point in putting more than $60k a year on the other Biz Amexes): the Gold has bonus categories (with an asterisk) on $150k a year of spend before becoming 1x, the Platinum and Reserve give bonuses for airfare (Platinum 5x through portal with 1.53 cpp cash out for airfare; Reserve 3x with DL) and the Platinum gives 1.5x on large individual purchases while the Reserve gives 1.5x on everything after you've hit a spend target. So there's a niche where the DL Business Reserve is plausibly the best single option for a free-spending small business that puts seven figures on the card (everything else is not much better of a reward or cut you off before that point).

(The elephant in the room is how much of that spending in recent years has been augmented by PPP/ERC...)