Why hasn't the false vacuum collapsed yet?

1) The universe isn’t old enough yet

There are a number of calculations of the decay rate or lifetime of the electroweak vacuum, like Chigusa, 2018 and Andreassen, 2018, and they conclude that the Universe is not old enough to have decayed, i.e. predicted lifetime around 10^161 years compared to current lifetime of around $10^9$ years.

There is also a paper by Khoury, 2019 that posits this lifetime is no coincidence, rather an indicator of near criticality. System near criticality usually has some kind of selection pressure, or can be modelled that way

2) The Standard Model is not valid all the way to the Planck scale

The papers in (1) above all make this point, as does the answer by @Mitchell Porter. Basically, the OP's paper on BH's is in this same category, although what that paper actually says is:

The importance of these results lies in the fact that a single primordial black hole in the observable universe would cause the decay of the Standard Model Higgs vacuum, and therefore would contradict the Standard Model.

i.e. maybe there are no primordial BH's, or the SM is not valid all the way to the Planck scale.

3) The vacuum is stable, but right on the critical boundary 

The Higgs and/or the top quark pole masses are slightly different to the current PDG running averages, and the Universe is actually stable, but right on the boundary of metastability, i.e. near criticality.

The masses of the Higgs and the top show that the parameters of the standard model are tuned such that the vacuum is on the edge of decay anyway. The reason for this is not at all known, and suggests that there are processes at work, perhaps at the quantum gravity scale, which are not accounted for in models like the one you cite.