There is absolutely no reason not to enjoy the perks of the early stage of the customer acquisition process; the shareholders are subsidizing your product at no cost to you.
At the individual level, sure. Even for things like streaming services it isn’t a net negative to take advantage of those ‘introductory’ prices.
But a lot of these businesses that operate at an obvious loss are undercutting currently existing business practices that are probably more cost efficient than these new businesses. Like restaurants that used to take care of their own delivery were undercut by malicious pricing from door dash and uber eats only to wind up in a situation where they would have to start from scratch again or pay the outrageous extortion fees to DD and UE.
I avoided both DD and UE because I knew it would not be sustainably long term. It was obvious they were maliciously undercutting competition. Same with uber and lyft and all the other ride share businesses, although at least they got some reform going on the taxi side.