You can always play with the factors. Maybe FTL is possible, but requires a sizable fraction of the planet's resources. Or you can eventually reach another plan

You can always play with the factors. Maybe FTL is possible, but requires a sizable fraction of the planet's resources. Or you can eventually reach another planet, but terraforming it and building the technology for creating more FTL ships will take millions of years. Basically: FTL is fast but pointless, because getting to FTL takes longer than getting to your destination. Maybe space is a bit more emptier than you think, and FTL is a bit slower. Or maybe it is busy, but we haven't waited long enough. I mean think of a native American in the 1400s. If transoceanic travel is possible, why haven't we seen visitors from other continents yet? Finally, it is still entirely possible that "they" are already there, and there is a cover up. I don't believe it (Occam's razor), but if FTL turns out to be theoretically possible, than I think I will have to update my beliefs :-)