It’s not just about the mass, but how strongly it couples to the things we can directly manipulate (typically, protons, electrons, muons and occasionally their anti-particles, and photons). The top quark, being a third generation quark turns out to be far easier to produce (if you work out the details of the standard model) than the Higgs. Yes, the heavier mass might act as a suppressor but stronger couplings act as an enabler.

So, a “dark matter” particle at even few GeV could have gone hitherto undetected, because it hardly talks to anything we can directly manipulate/sense (hence the “dark” moniker).