Size is important (heh). Democracy in ancient Athens had a "demos" only two or three orders of magnitude larger than Dunbar's number.

Let's ignore the "massification" of democracy (by which I mean entrenched power gaining leverage over the "demos" by targeting propaganda at the low-agency portion of the population, but this may be controversial?). Population scale has changed but Dunbar's number hasn't, and if the 0.1% of the population that is deeply invested in a topic manages to organize, there's a high likelihood that they can get critical reach. However, population scale has changed and Dunbar's number hasn't, so the first step of actually organizing 0.1% of the total population becomes a lot more difficult with scale.

Arguably, my distrust of modern democracy doesn't help, but I have no idea how anyone could manage to find and fish out 20k specific individuals from a pool of 20M people. And that's what needs to be done, IMO, not signing petitions (and in Canada, there's already a little bit of debanking-based chilling effect re: out-of-band political organization).