I really doubt it's that, as opposed to the maintenance cost of an extra flow to a boarding pass. Or perhaps just a perceived complexity/annoyance cost when something breaks in the desktop flow here and there.
I'd think it's only maybe 5-10% of customers at most who both use desktop over mobile to get their boarding pass and use an ad-blocker on desktop. And honestly I don't remember ever seeing an ad (even on Ryanair) when getting my boarding pass on mobile. OTOH I distinctly remember seeing many giant ads on printed boarding passes, most often on printed boarding passes brandished by other customers (usually printed in full color!). I'd think that's hugely more valuable as advertising real estate than the iota of additional data they get to collect on a few adblock users who have been forced to use mobile.
I'd think it's only maybe 5-10% of customers at most who both use desktop over mobile to get their boarding pass and use an ad-blocker on desktop. And honestly I don't remember ever seeing an ad (even on Ryanair) when getting my boarding pass on mobile. OTOH I distinctly remember seeing many giant ads on printed boarding passes, most often on printed boarding passes brandished by other customers (usually printed in full color!). I'd think that's hugely more valuable as advertising real estate than the iota of additional data they get to collect on a few adblock users who have been forced to use mobile.