It's probably because of the name. But most savvy people using H-E use other interfaces because there are no diesel pools on the Hive-Engine website.
And the difference in traffic is not that high. I wonder if people using the H-E website are doing that because of its simplicity, and they may be in a group reluctant to try something like leases.
It could also be the reason that there are many users who started out with HIVE-Engine and not interested in Diesel Pools yet.
That's possible, of course. I actually know someone who uses diesel pools on BSwap and still uses Hive-Engine for the rest because he likes it more than TribalDex.