The likely answer is to do with audience biases. A survey conducted by an email marketing provider is almost certainly going to have different results to one conducted by PPC management tool, as their audiences have different skillsets and biases, skewing the results of their sample. As such, we should take the specific ranking of different strategies in these studies with a pinch of salt.
Visitor Tracking: Hotjar has a heatmap tool — a virtual tool which creates a color-coded representation of how a user navigates your site — that helps you understand what users want, care about, and do on your site. It records visitors and tells you where they spend the most time on your site. You can use it to gather information on your lead generation forms, feedback forms and surveys, and more.
Leads may come from various sources or activities, for example, digitally via the Internet, through personal referrals, through telephone calls either by the company or telemarketers, through advertisements, and events. A 2015 study found that 89% of respondents cited email as the most-used channel for generating leads, followed by content marketing, search engine, and finally events. A study from 2014 found that direct traffic, search engines, and web referrals were the three most popular online channels for lead generation, accounting for 93% of leads.