Eh. The problem with being Trippier's age and a PL player is that you start to want to force yourself into your national team setup - especially at a club like Spurs, I can imagine it would be a bit depressing to see all your team-mates head off to international duty on the breaks (including your competitor for an RB slot) while you're entering the prime of your career with naught to show for it but a spot as a backup RB. Assume that a move to any new club brings with it a period of adjustment - all the more reason for Trippier to move now, so that he can get that iffy period out of the way and hit his stride by the time he turns 28-29, so that he can at least attempt to get a few caps via a regular starting spot for a PL club. Same goes with a possible move down to a lower club and then (if he performs well) a move back up to a bigger club when he's 28-29 - if that is to remain a possibility, he needs to leave while he's still 26-27 so he can impress at said lower club for at least a couple of seasons prior to the move back up.
Davies is younger, but the same dilemma presents itself to him - he probably has a better grip on the LB/CB role at Wales than Trippier does on the RB slot for Engand, but he has competitors (Neil Taylor for the LB slot, a range of players for that LCB position), and he isn't getting any younger. He's 23-24 now, so maybe if he moves back down to a lower club and gets regular football, he can move back up at 25-26 and then (if he continues performing well) move even higher up at 27-28 to conclude his career with a period spent playing for another Spurs-sized club (or perhaps an even bigger one). All of which would guarantee his selection for Wales more than sitting on the bench at Spurs would.
And then, of course, there are the wages and sponsorship deals to consider - more time spent playing regular first-team football would lead to higher wages over the medium term than sitting as a backup RB at Spurs, with our considerably strict wage policy. And the exposure would help both of them secure more lucrative sponsorship deals.
I'd like it if both of them stayed - there isn't much wrong with them as backups, although I wouldn't like to rely on either for too long a period. But there are reasons why there tends to be a regular churn of backup players at most clubs, and at a club of our size (fairly high up on the football ladder), the concerns laid out above are the chief reasons for that squad churn, imo. Part of the business - and I think it's probably safe to expect that our backups won't stay at the club for more than 2-3 years in most cases.