Because of the SPAM, your synchronization time is 100 times slower.
Zcash used to offer a fix fee for all shielded transactions regardless of their sizes: 0.00001 ZEC. That’s very cheap. One day, someone started making transactions with 1000s of inputs/outputs for next to nothing.
Thus, pretty much all the blocks got filled with garbage (most likely, it’s shielded - we do not know what is inside).
Eventually, fees were raised but that took one year, during which the SPAM went uncontrolled.
The SPAM lasted from block height 1 700 000 to 2 200 000 (roughly).
If you have to scan over that period, you will notice that the speed goes down to 1% of what it used to, as blocks are 100 times larger.
The good news is:
The bad news is: