It’s difficult to say for sure because many campaigns involve more than just a petition, so other factors come into play too.
For example, one Petition which was started by a student in 2015 was calling out to consider sanitary towels and tampons to be essential items and abolish charging VAT on them. The petition attracted over 300,000 signatures, so it was reported by other media outlets and it raised public awareness of the issue and led to more public protest.
VAT on these products was eventually abolished but it wasn’t just the petition that made the changes happen - other factors came into play too - but the petition played a part.
I guess many petitions are started just to vent disapproval about something that’s happening and, if enough people don’t bother to do anything else to campaign against it or add pressure on those in a position to make the change, then it’s unlikely to change anything.
