Why?
It’s very silly indeed…
There are cards in paper that make ooze tokens, none in Mtgpq though
I mean, none in any recent sets that I know of. So that’s why.
But the card itself makes ooze tokens in paper (same goes for Hatchery Spider, Thorn Lieutenant, and most of the other leaders), so they probably figured it was just easier to make it an Ooze leader.
No real need to read into it more than that.
True, but it’s wroth asking the question “Why was this poor design decision taken”?
I don’t think this is necessarily a poor design decision. Its a reasonable choice (since the card reinforces itself anyway), and since there is no real harm in doing it it makes sense on the off chance there are more ooze cards in the future
Yeah, I suppose so. I just don’t like Leader much 
It’s very much an ‘eggs in one basket’ mechanic…
Some people asked similar questions about the elf leader and wise voices said “Just wait… There will be elf tokens!” And, lo, Selesnya came and it was good.
And someone asked the same question about Hatchery spider and insects and wise voices said “just wait… there will be insects token!” And, lo, nothing came ———so far.
Izoni makes them, same set and same color. So does the locust god if you want backwards compatible.
Only problem there is the Selesnaya elf tokens are generally superior to the Elf leader.
FYI, The Locust God makes insect tokens.
Its makes Hatchery Spider ridiculous with Day’s Undoing