Why Google do the change SEO process very fastly?

[hoangvu]

Hello Guys,

Please let me know why Google changes to own SEO strategies for keyword ranking? I think this is very interesting question if you are doing online business through the Search Engine Optimizer. if there is any SEO, Google gave us many updates in last 3 years. 1. Google Panda 2. Google Penguin 3. EMD (Eject Match Domain).

But i am not getting to Google, why they are changing to SEO strategies and given many restriction on us?