Because ammo is not specifically mentioned in the SA. If you put a 1000% ammo and gun tax via Executive order, no one will afford the guns. Do not forget that Budget Reconciliation deal was used to push thru the ObamaCare, so the Republican House will be bypassed again.
It is already commercially feasible to make primers and powders with expiration dates, so reloaders will be left empty-handed.
If you think that it is far fetched, would you believe me 3 years ago if I had told that Our Glorious Leader would be re-elected, despite all the obvious lies, out of control spending, shredding of the Constitution on a daily basis? That supposedly "conservative" Chief Justice would become Our Glorious Leader's asswipe and vote for ObamaCare?
This is how it was done in other countries. The fewer folks that can afford to shoot, the fewer folks to complain about a ban.