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I was going to reply similarly - a Kardashev scale II or III civilization could do more with Von Neuman devices than we could. At that point, a probability analysis shifts from the rigors/cost of crossing interstellar space to how likely is a K2 or above society. An analysis for which data (that we puny humans could access) is lacking. In any case, I agree the probability of a VN seeded galaxy seems much higher than ET biological entities in ships that play peekaboo and have well-stocked proctology clinics. (though given healthcare costs in the States, could anyone complain about being snatched up for a free endoscopy session?)

The Von Neuman hypothesis strikes me as the most neutral in its assumptions: for whatever reason, advanced civs may send out self-replicating units in the millions (and thence to billions via replication) and they just blanket all star systems in the spectral range most hospitable to life. Or not. Other filters are possible. We can't say what cost/benefit ratio is determined by a K2-plus civilization, or if anthropological fascination has anything to do with it, or what ethos they may have about contact, or if carbon-based life is seen as interesting...or just an old-fashioned and disgusting fetish that preceded the Glorious Uploading. Or quaint, and as @Moontanman mentioned, a niche hobby for some tiny fraction that studies emerging sentience. If aliens were machine intelligences, they could have some form of immortality that would open up motivations we can't conceive of, where shutting down for a ten thousand year journey would be routine. Or a nice field trip for fourth graders.

Again, I do not assert UAP are aliens, they are unidentified, aliens is just one remote possibility, time travelers have been suggested as a possible explanation but I have my doubts about time travel as I am sure most people do. They could be visitors from another plane of existence, or as Jacques Vallée has suggested, quite seriously, that the UFO phenomena is connected with things like fairies, gnomes, and other supposed supernatural creatures from lore. The most obvious thing here is that UAP are just misidentification of known or unknown natural objects but the best data we have doesn't support that premise in many cases... it is these outliers that concern me. And no, "It could have been a picture of a hubcap someone threw", is not a viable explanation. As for alien motivations... you make a good point if you are talking about a civilization that is only a few thousand years since it lived in caves. A civilization that has existed for millions of years might have more long-term goals and data can be transmitted at the speed of light. Trying to guess the motivations of aliens is not a winning gambit.