The game industry has tried in-game advertising before. I personally worked on a game in the PS3/X360 era that was one of them. We learned a few things back then - advertisements tend not to work very well in games because the advertisers must track engagement in order to determine whether the advertising is effective. This usually means tracking how many players saw the ads and overall player watch time.
On the game I was working on, we only placed ads where it made sense within the world - in-game billboards and the like in cityscapes. As a result, the engagement numbers were dismal. Players might see the ad as they were playing, but they rarely actually looked at them. It was just background noise to them. Unless the Roblox advertising is somehow interactive (i.e. the advertisers pay to have special Roblox-specific content created for them), players will likely spend very little time engaging with those ads and even fewer of them will actually engage with them meaningfully.
The most effective advertisements today tend to be targeted ads on social media platforms. These are able to serve up ads based on context that the platform has gathered on you as a user - your interests, your purchasing habits, etc. Given how many of Roblox’s players are children (thus being off-limits to Roblox’s data-gathering thanks to laws like COPPA), I can’t see this particular decision be a particularly fruitful one.
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