Because they require 5.3B shares just in reserve. 4.2B suggests current O/S at around the 800M mark, which is also at the Nasdaq published share count.
The 4.2billion reserve shares covers the 120mm restricted principal on the remaining investor notes. (Calculate at a conversion price of approx 0.02)
1) the shares will only be issued if the investors pay the notes down and they want to convert to shares 2) if HMNY doesn't need some or all of the cash from investor notes they can redeem any outstanding balance on the notes or buy back shares.