Why speculate?
[ Source ]
If you look closely,
the various “3rd-party” offerings that are well integrated / promoted
(eg. Quicko, Tijori, Smallcase, Ditto, … including Sensibull)
are from companies that Zerodha / Rainmatter is a significant investor in.
Presumably as their stated/apparent goals align.
Source: Rainmatter by Zerodha – Indian fintech and health fund
For any 3rd-party company,
access to Zerodha’s user-base
is an excellent funnel to generate leads, test new features, engage in cross-selling/up-selling.