Among Uber’s strategies for world domination of the ride-sharing space has been partnering with travel-loyalty programs, including American AAdvantage, Hilton Honors, IHG Rewards, and Starwood Preferred Guest. It’s a sensible marketing approach: Members of travel-rewards programs are frequently on the road, in need of local transport, and they’re opinion-influencers by virtue of their deep experience.

That makes today’s Starwood announcement on Twitter that much more surprising:

Since 2015, SPG has offered you the opportunity to earn Starpoints for rides you take on Uber. The partnership will not be renewed for 2018 and will officially end on December 17, 2017. You don’t need to take any action. Your SPG account and the Starpoints you’ve earned to date with Uber will not be affected and you can still earn through December 17, 2017.

Neither company is likely to divulge the real reason for the split, or reveal which company precipitated it. But there are a number of possibilities. Among them:

• The economics of the relationship weren’t sufficiently favorable for Starwood. Adding credence to this theory is the fact that earlier this year, 1) the earning rate was reduced from one Starwood point per $1 charged on Uber rides to one point per $2 in spend, and 2) the bonus for Uber rides in conjunction with a Starwood stay was discontinued. Those changes suggest the tie-up was too spendy for Starwood.
• Uber’s reputation as a trusted travel partner and ethical operator has taken a hit recently, with a long series of allegations of corporate misdeeds and management turmoil.
• Marriott, which has acquired Starwood, may be working on a tie-up with Lyft, Uber’s primary competitor, which would rule out an Uber relationship on competitive grounds.

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Whatever the reason or reasons, Starwood Preferred Guest members have until December 17 to earn points for their Uber rides.

After 20 years working in the travel industry, and almost that long writing about it, Tim Winship knows a thing or two about travel. Follow him on Twitter @twinship.

This article first appeared on SmarterTravel.com, where Tim is Editor-at-Large.