I suspect Waymo has purchased all available Jaguar i-Paces (~= every Jaguar i-Pace?), which are no longer in production, and was planning on rolling out their purpose-built Zeekr vehicles to scale further. The 100% tariff on Chinese EVs introduced in 2024 probably made this plan financially questionable, leaving them without a supply of new vehicles. Late last year Waymo announced a partnership with Hyundai to buy a version of the Ioniq 5 assembled in the US which might've been motivated by this problem.

The Zeekr vehicle was announced in 2021: https://waymo.com/blog/2021/12/expanding-our-waymo-one-fleet...

100% tariff in 2024: https://www.theguardian.com/business/article/2024/may/14/joe... ; https://www.reuters.com/business/us-locks-steep-china-tariff...

Hyundai partnership announced a few months later: https://waymo.com/blog/2024/10/waymo-and-hyundai-enter-partn...

Plus what others have said about sheer number of vehicles not being the only obstacle to scaling.