Some start-up background on this company:
https://www.tnooz.com/article/startup-pitch-stride-applies-metasearch-to-tours-and-adventure-travel/
This stood out for me:
"Suppliers should work with Stride because we prominently highlight, rather than hide, the operator brand"
"If you look at multi-day tours, there are several specialty OTAs (online travel agency) some who transitioned from being traditional offline travel agencies. However, their model is different. As OTAs they are incentivized to hide the supplier brand name and induce users to book on their site with their small number of preferred tour operators."
The "hide the operator" tactic of 3rd party day-tour bookers - like Viator - seriously bugs me and is a reason I don't use them. It doesn't allow you to research background and reviews on those operators, and replaces their partners' identities with the 3rd-party brand.
I'm pretty sure that the "quality" brands listed on the site would not have agreed to partner under this sort of model: their brand names are too valuable.
And this:
"No search engines existed for multi-day tours and adventure trips and the major reviews websites did not have a category for this type of travel... TripAdvisor is a big ‘competitor’ in terms of general traveler expectations around reviews. However they do not have a category for multi-day tour operators and actually specifically prohibit multi-day tour operators on their listing page qualifications."
OK, that makes sense.
I'm guessing partner costs are on a per-click metadata model that brings the potential customer from the search-engine site directly to their own. It's possible that there's also some tracking going on that can be really useful to a business: which of their tours are getting the most clicks (exposure/interest), which other companies potential customers are clicking on in conjunction (e.g. identifying closest competitors) and stuff like that.
Believe it or not, there are likely inexperienced travelers out there who know that RS produces guidebooks but don't know that they also operate tours so added exposure for those is a plus.
Advertising and research budgets are the price of operating a competitive business. :O)