Buying a PC game frequently means installing another application to run it. The proliferation of launchers follows from what a storefront actually controls.
The storefront fee is the visible reason
Digital stores retain a share of every sale, and on a large release that share is a substantial sum flowing to a company that did not make the game.
Selling directly removes that cut entirely, and for a publisher with several large titles the annual difference justifies building and staffing a store.
The saving is real but overstated as a motive, because running a storefront carries its own costs in payment processing, support and infrastructure.
Customer data is the more valuable asset
A publisher selling through someone else's store sees sales figures and little else, while the store sees who bought, what else they own and how they behave.
Owning the storefront means owning that data, which enables direct marketing, targeted offers and the ability to reach players without paying an intermediary.
For live service games in particular, the ongoing relationship is worth far more than the margin on the initial purchase.
Live games need infrastructure the storefront does not provide
Accounts, friend lists, progression, anti-cheat and cross-platform identity all have to exist independently of any single store if a game runs on several platforms.
Once that account system exists, a launcher is a thin addition, and the publisher is no longer dependent on a third party for authentication or patching.
This is why launchers appear most often around games with persistent progression and least often around single-player releases.
Exclusivity was used to force adoption
A new storefront has no reason for anyone to install it, so several have paid for exclusive release windows to give players no alternative.
That approach builds an installed base quickly and generates considerable resentment, since the player receives no benefit from the arrangement.
The tactic has faded as stores have matured, but it established the pattern of a launcher being something imposed rather than chosen.
The costs land on the player
Every additional launcher means another account, another update process, another background application and another place where a library is fragmented.
Games that require two launchers to start, one to purchase and one to run, are the clearest illustration of an arrangement built around business boundaries rather than use.
Some publishers have responded by returning to the larger stores while keeping their account system underneath, which preserves the relationship without demanding a separate application.