[Antilochos]

That last sentence; it still keeps me puzzled why Verstappen signed for such a long period. He could of choose any team he liked I believe.
Unless, he agreed a clause that if car cq. engine is not compatible for championship, he can walk. Horner nor Verstappen will ever tell you early of this clause.

For Ricciardo, I'm not so sure he has as many options as Verstappen. Not saying Verstappen is that much better, but Verstappen has a exponential grow curve ánd is very young. Great combo for teams. As a bonus, he already is a star.
Ricciardo on the other hand is very reliable, fast and also a star. But he reached his peak already (or there is not much grow left) and is moving into the autumn of his career (at least I think that). Yes, he might be able to catch a championship, but Verstappen has the potential for a team to catch multiple championships.
In short, Verstappen is long term investment and Ricciardo short term (in team perspective). With Vettel and Hamilton already there, a short term investment might not be worth it for the teams.

Option for Ricciardo; early retirement (out of F1) of Alonso and Renault engine becomes better, McLaren could be a team for him.
Vettel in Ferrari, Hamilton in Mercedes, Verstappen in Red Bull and Riccardo in McLaren. Would love a fight for championship like this.