ʻOumuamua was discovered on October 19, 2017, and 2I/Borisov was discovered on August 30, 2019. Has something changed about observation techniques or equipment that made it possible to find these objects in less than two years?
I find it hard to believe that there has been no interstellar objects passing through the inner solar system in the past ten or twenty years, then suddently these two did, quite close in time.
I recognize it is incredibly hard to find such small, dark objects moving so fast, especially if they are outside of the ecliptic, and there be many more passing through that just haven't been discovered. Should this be chalked up to pure luck?