I've made a wsp package from design manager and imported it into visual studio.
When I'm editing the html page layouts the aspx file doesn't get updated.. What do I miss?
You cannot do it like that. Visual Studio will not convert your HTML design files into .aspx. You can only do that conversion through SharePoint's Design Manager functionality.
If you need real-time converting html to aspx, you can map network drive to masterpages folder, open and edit html file. Aspx file will be updated right after saving html.