I kind of agree with you, buuuuuuut if not aliens what could they be?
In my heart I want them to be aliens.
First off, we live in a competitive system where people are forced to 'get ahead' of each other.
Information, resource and technology sharing is not a high priority... its tightly controlled for the purpose of 'getting ahead'.
Also, people who are 'experts' in their field don't know every single bit of information in that field... at best, they may acquire 0.000001% of information in that area for the duration of their studies... and would take them literally millions of years of uninterrupted studying to catch up to what we know now in just that one field (never-mind the fact that new information in any given field is coming out every single day).
Oh and, in order to even begin identifying something unknown, you can't have 'experts' in a single field... you'd need generalists who have acquired information in several different fields - because such people can more easily 'make connections' rather than disconnected specialists.
Things to note: we had the ability to create synthetic metamaterials with adaptive properties that can be made in sustainable abundance with minimal impact to the environment a LONG time ago (since 1970-ies).
Better materials as we know can lead to far better efficiency, maneuverability, and a host of other different things that you can probably imagine.
You might be shocked to learn what was possible to create in 1970-ies using technology, resources and knowledge of that era alone when 'money' is taken out of equation and you focus on available resources, latest science and technology to get a job done.
Its also important to NOT jump to conclusions.
UFO = unidentified flying object. It does NOT mean 'aliens'.
What you 'want' to think is immaterial.
Any sufficiently advanced species capable of FTL travel would probably NOT have a need to park themselves in low orbit... they'd likely be able to get all the information they need on us from not getting anywhere close to Earth - especially if we factor in law of accelerating returns.
UFO's are likely as of yet unidentified human made objects.