Writing my dissertation here in the UK and can’t seem to find any other ways of saying the above. Any help is welcome, thank you for your time.
From Wikipedia:
A proximate cause is an event which is closest to, or immediately responsible for causing, some observed result. This exists in contrast to a higher-level ultimate cause (or distal cause) which is usually thought of as the "real" reason something occurred.
If the reason offered is a plausible fake, with bad intent, then you're talking about a pretext.
pretext: a purpose or motive alleged or an appearance assumed in order to cloak the real intention or state of affairs
https://www.merriam-webster.com/dictionary/pretext
If, as the example in your post implies, the reason given is just simpler or easier to understand, then I think you probably can't outdo superficial reason as describing exactly what you're talking about.
There is also putative reason, but a putative reason is a pretext.