The reason behind the change is that because mobile and desktop versions of pages usually vary widely, it tends to confuse mobile users who end up viewing search results that are better optimised for desktops.
The bigger picture here is that Google wants to "encourage webmasters to make their content mobile-friendly".
Google's director of engineering Cathy Edwards says in the blog that users can expect to see a lot more GIFs on Google services in the near future, and noted that Google images has become more about self-expression in addition to finding photo information. Terms of the deal weren't disclosed.
Tenor was founded in 2014 and has rapidly cemented its foothold in the GIF focused platforms. Tenor has easily been the most downloaded app on both Android and iOS with Giphy being among its immediate rivals. "Since early 2017, GIF searches on Tenor have grown by 5X in key markets like Europe, South America and Southeast Asia, in part due to Tenor's investment in providing localized regional search content", the company said in a blog post last month. Tenor now powers a large portion of gif searches within apps and chat services; most notably those on Facebook Messenger. In 2015, Tenor launched a GIF keyboard to help users "express any emotion" through the file format.
However, Google did say in its announcement that Tenor will keep its separate brand and that Google is "looking forward to investing in their technology and relationships with content and API partners". The platform also has existing integrations with a large number of applications, including Gboard, Facebook Messenger, WhatsApp, Twitter, Kik, Viber, Zynga, and Samsung Messages.