One restaurant leaving the platform will likely be much worse for that restaurant, but many leaving the scheme will be worse for the platform. No one restaurant has much bargaining power to demand better terms, but many together may be able to bargain better.
It seems to me like this is exactly how they demand better terms and change the balance of power in the relationship.
One could say that the platform putting such strain on the restaurants is manipulative because they know that it's very difficult for any restaurant to say no. I think it's just how the market works and think it's great that the restaurants are managing to push back somewhat.
It seems somewhat distasteful to argue that the pricing power of the rich, powerful party should not be countered by the weaker, poorer party improving their pricing power - especially on a moral basis.
Aren't the apps negotiating terms essentially a 'manipulative social movement' with a single app/VC backer/organizer (each)? why shouldn't the restaurant owners organize in order to increase their bargaining power to match?
What they're doing instead is telling the media they've been cheated - that they deserve more money, and Zomato's acting unethically by giving them the advertised service for the agreed price. I'm not sure that's an honest way to look at the situation.
If FTC allows restaurant owners (or any group of businesses) to create pacts like this against their suppliers or customers, next time, they will make similar pacts against you (the customer). "hey, what say, let's all make a pact together and increase the price of that dosa to $50?"
In reality, some industries (most famously airlines) do this kind of collusion through winks and nods anyway and is bad for consumers (very good for the industry as a whole though).