Another part of the reason is that in every company I have ever worked for some SEO dude insists we need to add literally 10 different tracking scripts and insists they need to load first and consume megabytes of data. At my last gig the landing page was 190kb of HTML, CSS and JS from us, 800kb of images and literally 8mb in vendor scripts we were mandated to load as early as possible. Of course we fought it, of course nobody cared.