Australia

More likely that change.org provides information about who signed (including emails unless opted out) to the person running the petition. Information gathering from informal petitions is more likely to undermine trust and make people less likely to sign, but then you can't build a database of people sympathetic to some cause and spam them afterwards.

The "20,000 petition signatures" feels like straight up manipulation - there's no magic number to force a debate at parliament, and as MisterFrog@aussie.zone points out, an official petition would be needed for it to be tabled. If an official petition with a lot of signatures is tabled, that is a signal to politicians that the public care about it, and can overcome lobbying in the other direction and apathy, so it increases the chance a bill is put up for debate.

This comes from an ad agency; they don't list any gambling companies as clients, but I'm sure they'd find information like a list of people who signed useful for something.

That said, it's still a good idea to regulate in a losing sound if there is no political will to do anything more drastic. Better yet would be to require linking play to a one-per-person card, and having hourly, daily, monthly and annual loss limits per card, after which the owner cannot allow any more losses for that card holder.