I agree with Toast's answer.

I'd like to add that the larger all-out maxed army battles you commonly see are also an artifact of the maps that are currently used in ladder. 

The current ladder maps feature the following traits that lead to large macro games,

 - Main base is on high ground
 - Main bases are at the edges of the map and far apart from each other
 - Narrow ramp leading to main base
 - Close natural expansion
 - Easy to defend choke in front of natural expansion
 - 3rd expansion close to main base
 - Has a high number of extra expansions

I looked for counterexamples to these traits in current SC2 maps, but I couldn't find any. So please bear with the Brood War examples =P

> Andromeda (2008)

![Andromeda][1]

Meet "Andromeda"; this is a macro map. Games generally lasted 40+ minutes.

 - Main base is on high ground ✔
 - Main bases are at the edges of the map and far apart from each other ✔
 - Narrow ramp leading to main base ✔
 - Close natural expansion ✔ (*It's **in** your main*)
 - Easy to defend choke in front of natural expansion ✔
 - 3rd expansion close to main base ✔
 - Has a high number of extra expansions ✔ (*7 for each player*)

Throw in the vast openness of the center of the map, and this map was perfect for defensive play. The games focused on denying and trading expansions.

> Bifrost (2002)

![Bifrost][2]

Say Hello to "Bifrost"; this is a micro map.

 - Main base is on high ground ✘
 - Main bases are at the edges of the map and far apart from each other ✘
 - Narrow ramp leading to main base ✘
 - Close natural expansion ✔/✘ (*There's a mineral-only behind the main. But to get gas, you had to stretch*)
 - Easy to defend choke in front of natural expansion ✘ (*It has two routes of attack; and one route is from the high ground! Commit to defending your natural, and your main is vulnerable*)
 - 3rd expansion close to main base ✘ (*It's the same land distance to the 3rd gas as to your opponent's door*)
 - Has a high number of extra expansions ✘ (*2 with gas for each player*)

Never had the pleasure to see a game on this map (was before my time). But just looking at the attack routes and limited gas on the map, I'd guess that it was rare to see maxed armies or even tier 3 units on this map.


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It's helpful to think about what playstyles the maps will inherently favor.

  [1]: https://i.sstatic.net/kLgKU.jpg
  [2]: https://i.sstatic.net/21VOB.jpg