The number of UK Government and Parliament petitions that have led to an identifiable policy change is so small as to be statistically negligible — effectively a rounding error compared with the total number submitted.

Right but a policy change isn't the guarentee offered just the debate. Getting to a debate is a win! Despite no concrete policy changes it doesn't mean there won't be other second order effects from having this bought to peoples attention.

If you think we're going to have government by petition then I don't know what to tell you.