Answer: Because market share isn't as important as you think it is.
Market share is simply the percentage of things sold over the last quarter. ALL things.
Tablet market share includes iPads, Samsung tablets, Asus tablets, and all those cheap terrible tablets sold around the world.
But Android tablets make up a lot of units sold and thus a huge percentage of market share... so that's the clear winner, right?
Not so fast.
You can't just look at market share and make a decision based on that. You also have to consider the customers who might buy your app.
Developers don't care how many units are sold... developers will go where there is a better chance to make money.
And it's been like that for a long time. For instance... the iPhone has NEVER had more than 25% smartphone market share. And yet... it's always been a hugely successful platform.
Because iPhone customers spend more money on apps, games and accessories. It doesn't matter what their market share happens to be. And the same is true for tablets.
The iPad may only have 34% of the tablet market... but there's a better chance you'll be able to sell your app.