For comparison, the initial completion of the HBLR cost around $2.2 Billon (~$3.7 Billon adj inflation). You could build almost 3 new lines which would lead to even more development and tax revenue than this project. Additionally, HBLR is at, may even be over, capacity as daily ridership is at ~52K per day (2017). IIRC, the HBLR was to have a capacity of about 40K daily riders although I can't find that information now.

Plus, IIRC this current plan would take about 10 years to complete and would undoubtedly cause even more traffic as there is already construction happening between the Newark and Bayonne portion. So they are fine with being in more traffic for about 10 years in order to alleviate traffic for the1-2 years after its done then we're back to square one.