doubt in pagelayouts while upgrade from SharePoint 2007 to SharePoint 2013

We did database detach and attach method to migrate SharePoint 2007 to SharePoint 2010 to SharePoint 2013.

After migrating to SharePoint 2013 when i open the site in SharePoint Designer 2013. i don't see .html pages for Master Pages and Page Layouts.

Usually when you create Master page and Page layouts in SharePoint 2013 using Desgin Manager we get .html files along with Master pages and Page Layouts right ??

then why not when we migrate site using database attach and detach method.

without html files how do i modify master pages and page layouts because i read we should only customisation .html files in SharePoint 2013.

Thanks,

M.M