You brought it up as an example of spending serious money on a telescope.
Implied it? I told you that I wouldn't mind spending more on planetary defense but not the sort of money you'd just mentioned when you brought up that JWST had cost $10 billion. What I was rejecting from you was your apparent claim that we could not both fight global warming and conduct adequate planetary defense simultaneously
Impacts are slightly periodic but not for that reason. Bodies from the Oort Cloud and the Asteroid Belt get dislodged from their stable orbits by the passage of massive objects. Neither belt come near the Earth and neither belt cyclically changes position. Near Earth asteroids are primarily bodies from the Asteroid Belt (between Mars and Jupiter) that are "moved into the Inner Solar System through resonances with Jupiter"
Near-Earth object - Wikipedia