This is not that fast.
The first 120,000 blocks are contained in a single blk file (128M) because most of them are empty: Most do not include any transaction beside coinbase. In fact, at this point, you downloaded the 2 first blk file at this point, which is 0.1% of the whole blockchain (there is ~1300 block files as of today). As you'll meet bigger & bigger blocks, the process will go slower & slower.