Hamilton praises DR for the move
https://www.autosport.com/f1/news/138351/hamilton-lauds-brave-ricciardo-renault-risk
Historically F1 is a very mercenary sport. Drivers sticking to one team is rare, and usually reserved for midfield drivers who aren't good enough to get a better car, and midfield teams who aren't good enough to attract a better driver.
It's only recently where the sport has had a stable 'big three' teams, and a core of drivers that are probably interchangeable in terms of overall skill. (I'm happy to debate who's the best, but given the right car, Hamilton, Vettel, Ricciardo, Max (with patience) and Alonso are clearly champion material. Kimi, LeClerc, Ocon and Gasly woudn't surprise anyone either). Since I started watching F1 Alonso, Button, Hill and Schumacher all left teams as champions to 'take a risk'.