It's an interesting problem for Adobe, obviously they have huge inertia behind their products, it's hard to change from a tool you have been using for a long time. On the other hand they are a big corporation that needs feeding, they can't afford to give away their main product.

It isn't just Sketch, there are a whole bunch of developers nipping away at their heels. Many of them offer quality products that are good enough, especially for new users.

I wouldn't bet on Adobe looking anything like it does now in ten or fifteen years time.