Because it is a terrible porc map.

No good reason. Sandcastles is also a terrible porc map.

Irish: Having your own base that you defend is the point of these FFA maps. If you want ones where people actually attack early on, there are other maps for that (like Hotstepper or Mearth 4).

I don't see any problem with maps that include porcy start-areas as long as they give you plenty of incentive to move beyond the walls.

This one has an obscene amount of metal in the middle, so it's got that covered. The guy who hides in his base won't win this.

The metal level is too high, and the layout is too simplistic (4 fortresses and a kill-the-middle) but it could be workable with the right metal-adjustments.

all passage exits are quite difficult to path, there's a fix with much reduced height range

This looks very promising to me as a free-for-all map, with some nice defensive terrain in each of the castles themselves (including moats, ramparts, turrets, and even zwingers (also called corridors of death) combined with bent entrances (that are ideal for placing short-ranged units or structures around the bends for effective defense, whilst protecting them from artillery fire).

Of course, the map also encourages players to expand outside of their castle walls, since there's plenty of mexes to claim out there, especially in the center of the map. Although the castle walls provide an incredible degree of defense, they alone can't stop a player that's determined to besiege them, especially if they decide to use the otherwise rarely-used Quake missiles to make those castle walls crumble down into rubble (and that's in addition to using superweapons of course). Moreover, for as steep as the castle walls are, that won't stop spiders (including Scorpions and Funnelwebs) from scaling them.

The only ways that I could see this map improved with relatively little effort is these:
- 1. The center could do with far fewer mexes. I'd say cut the centermost mex count down from 16 to just 4, and cut the rimward mexes down from 16 to 8.
- 2. I'm a bit concerned about how narrow the bridges and corridors are, and how they could easily cause traffic jams when multiple striders start hitting the field. Maybe they'd be better off if they were made wide enough to allow a couple of Detriments to reliably pass around eachother as they move in opposite directions?

Overall, I think I'd rate this map 4/5 stars. It shows great promise, and is very nicely detailed, but is held back by some flaws in functionality and balance.