The general idea for higher user retention is increasing the number of live players in-game. Users are attracted to games with higher player counts; preferably a player count that fills up one or more servers. No matter how fun the game is, a small player count (or none at all) is not appealing. This is even more of an issue if the game requires multiple people to be able to play.
Currently, sponsors and advertisements work by having them shown evenly across the day. This is a problem for developers who cannot spend hundreds of thousands of Robux on advertising, as their ads will only show up occasionally, thereby receiving a trickle of players across the day. This is problematic, as discussed above.
If Roblox can add a system where an advertisement or sponsor can be shown with the entire budget spent in 1 hour (preferably also configurable), it would greatly improve the peak player count an up-and-coming game could receive. This is because all the players that would’ve clicked on the sponsor would do so in higher concentrations, in contrast to the trickle of players of the current system today.