Why are there so many glides in doom 2 iwads?

[Cilian]

So I watched a speedrun of doom 2 and plutonia and I was surprised with how many glides are possible in these iwads (doom 2 map 02 red key skip for example), so many that it feels lile they were added by map creators on purpose. If they made them unknowingly how did they do it and so often?

[RjY]

I think in the era in which Doom2 and Plutonia were made it was not yet known that the player could pass a 32 unit gap.

My recollection of nineties mapping literature and community "common wisdom" was that for a gap to be traversable by the player it needed to be at least 33 units wide. In particular, the influential Unofficial Doom Specs states
 

Quote

I don't know why the horizontal size is "slightly more" than 2 times
the radius, but it is. A player cannot enter a corridor of width 32, but
can enter a corridor of width 33. Experiments have shown that no monster
can enter a corridor that is exactly (2*radius) wide. It must be bigger.

So, many wads were made under the assumption that a 32 unit gap between bars was a sufficient barrier.

It was not until 1999 that glides/squeezes were discovered (cf. lv16-023.txt). It took several more years for this knowledge to permeate the community (witness TVR!, released 2003, full of 32 unit glides).
 

[baja blast rd.]

Additionally, Doom textures work in units of 2^n (16, 32, 64, 128), and the most often used grid sizes accordingly would also be 2^n -- so unless you know about and want to avoid glides, a lot of designs will almost effortlessly end up having them.

 

192-unit hole, 128-wide 'slab' (a natural length for a texture) in the center to block it off? That's a glide. 128 with 64-wide? Same thing. And that's just a couple examples. 

 

They're even still present the work of modern-day mappers who might not be aware of them.

[Murdoch]

My recollection may be inaccurate but I believe speedrunning techniques have developed over time, including gliding. Therefore, the ample opportunities to deploy the technique in Doom 2 were just a complete fluke.