While Zerodha's products fall under the investment tech umbrella, they differ considerably and cannot be combined into one universal app. The reasons for this are:

Business reasons

Kite, the trading platform, is built for fast intraday trading. Uptime is everything owing to its real-time nature. Coin, the mutual fund platform, is built for passive investment. They have different screens, buttons, toggles, icons, and other visual elements (UI) and user experience (UX). Both these apps are aimed at different market segments. Combining them would clutter the app with information, features, buttons etc, that may only be applicable to some market segments.

Active traders access Kite for several hours daily, while mutual fund investors open the Coin app at leisure. The business use cases and UX on these two applications are fundamentally different, and to a large extent, so are the target markets.

Keeping these products separate and giving them individual identities allows for constant improvement without worrying about other products. All applications are deep-linked to keep things user-friendly. They all have a single login and are linked to each other carefully in the proper contexts.

This is how Zerodha has built the plug-and-play Kite Connect ecosystem, which enables Zerodha, aspiring developers and startups, to be creative with new products. They plug into the ecosystem seamlessly without disrupting the core applications. Smallcase, Streak, and Sensibull are all applications built by different companies. They are free to build and run their businesses as they see fit, as they can plug and play.

Technical reasons

The underlying technologies, stacks and infrastructure required for Kite and Coin differ. Kite may internally get several updates per day, whereas Coin may get updates once every week. If they were one app, every time something changed, the entire application would have to be updated for everyone, which is impractical.

If a bug with Coin was reported and the applications were combined, it would affect trading on Kite.  Adding features would be highly complex, and the number of new unknown pathways where something can go wrong would be high.