Exactly out of the reasons you are stateing they should already have a strategy and concept how they want to get user into their PlayMarket, otherwise they will lose ground fast out there.

The reason I am asking is, because it seems like a very hard job to attract google users to another platform. Advertising is the minimum of what they should do, but I was hoping for concrete plans on this. I think they should do more than just advertising. For example; Giving away free stuff/sponsoring developers with their apps and make it available only on Playmarket.

I don't think it is like that.

There are too many game apps that have the option to gain money from it and Google is not allowing that. There is probably some more area google don't let it but it is not the black market.

Google require a one time fee of 25$ to start publishing your apps. Then they get 30% of the profit generated by you app if any.

If you want to avoid dumping apps at their platform 25$ is a bit low ... that's something a school kid can offord with his pocket money lol
To attract developer, sure it's one point to lower the fee, but also to have a big enough userbase. If they don't have enough user, why should developer go to PlayMarket? 25$ is nothing for an developer and if they have the chance to get much more income through the official app store, even with higher percentage, they probably will choose this. But maybe I am wrong. Maybe there is need for another store.

Beside this, there is of course the need of an alternative to google in every case. 
And it would be good, to have two or three other stores with better conditions related to earn money.

yes an alternative is always useful anyway I believe migration happens by degrees first they will create a considerable user pool so with a lot of userbase and low fee they can attract developers to publish new apps on the market...

They probably implement some but not they won't be strict like google.

Well user base is going to be the first hurdle that we have to tackle for sure. But if it is done cleverly by rewarding early participants or something, it is not a problem for long. I am pretty sure that this can't fight with google for the userbase but we only need a small share of it. The ones that user cryptocurrencies as a payment for starters.

yes or lil indi games developer can bring their product on the man for a low price.