Captcha typically adjusts itself based on your network or computers “reputation” ie is there a history of your IP address or account spamming features or doing suspicious things.
In terms of posting to group walls and such, it makes more sense to just not use a captcha unless there is suspicion something is going on. Ie a lot of people are posting to the wall, or a lot of accounts from your network are.
There is no reason someone in good standing should still get ridiculous Captchas. My best guess is that Roblox didn’t want to take any risks of people getting around this but it’s definitely possible to adjust it.