You might be confusing Gigabits for Gigabytes. 6 Gbps means 6 gigabit/s which translates to about 550 megabyte/s sequential in practice.
M.2 PCIe 3.0 x4 is 32 Gbps (4 GB/s), the same with PCIe 4.0 is about 64 Gbps, and PCIe 5.0 gives you 128 Gbps. 5/10/20 times faster than SATA 3, respectively.
Hard drives manage a bit above 250 MB/s nowadays, sequential. MLC and TLC SATA SSDs can usually saturate the interface, but QLC SSDs are generally much slower with write speeds between 50 and 150 MB/s.
SATA is 6 Gbps, not 6 GBps. Tiny cheap drives like the ones in this article are the only ones that struggle to saturate a SATA link during sequential transfers. Any NVMe drive 1TB or larger will offer sequential read performance several times higher than SATA could handle, and if it's a TLC drive rather than QLC the sequential write performance will also generally be at or above the SATA limit even after the SLC cache runs out.
A $50 budget NVMe will do that 5x over on cached writes or reads just fine. Remember SATA is 6 gigaBITS per second and drive speeds are often measured in BYTES per second. After overhead you only get ~500 MB/s if your SSD is attached via SATA, quite a few of the dirt cheap SATA drives in the article even seem to be running into that limitation at first.
There are architectural reasons for moving away from SATA I know, but the raw bandwidth is there.