Google Tag Manager not present on SaaS trial page

Problem

There is no Google Tag Manager code on the SaaS trial page (https://gitlab.com/-/trials/new) and seemingly on other pages in the SaaS flow (needs clarificatgion from @dennischarukulvanich).

Technical analysis

After initial analysis it seems that some templates related to trial flows do not share the same set of Javascript includes. I found one template that doesn't have the GTM code and produces a Javascript includes that can be seen in /-/trials/new:

https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/views/subscriptions/trials/_lead_form.html.haml

This seems to have been modified and GTM codes removed - could be potential cause, but needs more investigation.