Hmmm... where were these law firms weeks ago when all this was kicking off? Why didn't they get on tv and media to inform people of their rights back then? Or were they holding off so they could make some $$ from a class action?
As a lawyer who prefers to spend my time being an av-geek, the answer to your last question is "maybe", but here are some other potential reasons. Remember that class actions involve a lot of steps in court before a case is ever heard at trial and a LOT of initial upfront costs by the law firms with generally zero reward - at all - until and unless they win or settle for an amount that's worth their time and investment:
1) Despite the clarity in some airlines' terms (like Qantas) that refunds had to be given, many airlines and providers didn't have that clarity so the the outcome falls to general consumer law. There was a lot of uncertainty and speculation about how the Australian Competition and Consumer Commission was going to approach this, even though it still seemed on its face that refunds were due. Any sensible lawyer would need to hold off until that was clear, and the wait has paid off: the ACCC has now confirmed that refunds are owed, so the relatively weak argument that Virgin, Flight Centre, etc., were making holds absolutely no weight now.
2) Offering a credit initially but still allowing for a refund when pushed does not appear to be a contractual breach. If they muddle it up to the point of misrepresentation or bad faith (tougher to prove as airlines are clever in how they do this), then it's a problem, but simply staying silent on it and either waiting for passengers to request it or burying it within the terms of a voucher (as Qantas has done) is an obvious commercial ploy but not an obvious contractual breach. Still a case to be made, but not as tasty, and many firms wouldn't want to take that case until they were satisfied they had a good one with a bit more meat to it.
3) Law firms are hurting a lot in the current economic situation. It may simply be that the opportunity cost of taking a case that isn't a guarantee is less than it was a month ago when they had more work, so they're now willing to take the chance and go for it.
4) I was stunned at the lack of coverage on people's contractual rights when this began. I can see why airlines were pushing the vouchers, but it got to the point where it felt as though every major media outlet and online publication was pushing the same narrative and actively ignoring anyone who brought this up (had a lovely time being scolded by a defensive editor on ExecutiveTraveller myself, for the offence of pointing out in the comments that yes, people were entitled to a refund if Qantas cancelled their flight and linking to the Conditions of Carriage). No idea why / how that all happened, unless all those reporters / authors were just genuinely too lazy to actually look into the terms.
My first impulse when I saw the class action news yesterday was still a bit of, "meh." Not convinced yet, at least with most carriers in Australia (VA excepted, but that's obviously another legal issue now).
. I could have used the points for the BBQ in the Qantas store, but that would have returned less than 0.5 cents per point, even with 10% off for my "Points Plus" super status 
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