My understanding on this is that Apple is expanding existing contracts. Some involve doubling billion dollar contracts which adds up faster than this deal.
One of the things they announced when they made the original pledge was 20k for new high income jobs which is easily billions per year in salaries. Plus this requires expanding their various campuses because they do not allow work from home, so several more billion there.
These tech companies are massive so expanding their existing footprints adds up very quickly. Other mega tech corps like Meta and Google are increase spending by tens of billions just on AI expansion, however they haven't pledge that be specific to the US.
Become a security research and they will