Why isn't Executor permanently in the Journey Guide?

seems unlikely 

it currently takes about two years to get Executor to 7 stars if you are not paying crystals

having it available once each day changes that to less than a month 

The initial 4-star unlock event should be permanently available in the journey guide after one year, like Grand Inquisitor, Jar Jar, Jedi Cal, etc. The monthly event that pops up can stay exactly the same, where you either wait 2 years for a 7-star ship or spend the crystals. 

Of course, CG will never do this, same as accelerated ship shards won't happen.

Because you can't get the top fleet when you want it)

In the grand scheme of it, without the bonus tier does it matter when you unlock? Does a 4 star Leviathan do much? I took mine straight to 7 star by hoarding crystals so I needed the event for the rest of the shards. I did the same for Executor when it came out as 4 star really did not do much. I believe at the time it was known to take Executor to 5 star at least to be viable.

To clarify, I already have the Exec at 4 stars but was curious why it's still not a permanent addition in the Journey Guide. You raise an interesting point, though - I don't think the Executor is especially viable at only four or even five stars, because the level 8 upgrades on all the specials (including ult) are extremely useful.

And it would be very helpful to have the bonus tier roll around a little more frequently. 2 years just to get three additional stars on a ship is wild to me.

And it would be very helpful to have the bonus tier roll around a little more frequently. 2 years just to get three additional stars on a ship is wild to me.

Save up your crystals and do multiple refreshes the next time the event comes back, just like others before you have been doing