Does that make them have an ECS? I don't know for sure, but I don't think so.
Since most auction houses that produce a catalog (as opposed to eBay) tend to deal with tobacco cards, vintage (pre-WWII), 1950's and then some of the 1960's and 1970's, one has to look at the cards that were produced.
Professional Baseball was East Coast centric for the first 58 years of the 20th century.
Note: I'm painting with a broad brush here. This post is not meant to authoritative, just some general observations.
The Dodgers moved from Brooklyn to LA in the late 1950s. The expansion boom of the early 1960's pushed more teams west of the Mississippi. But I don't think that they really took hold in the hearts of most baseball fans that were card collectors.
I'm guessing that the majority of the population centers for the US were mostly on the East Coast. Yes, the West Coast teams grew in popularity, but the East Coast had a foothold.
Think of the great ball players of the 1950's and 1960's. Name them out loud. Who did they play for? Boston, New York. Brooklyn.
This is not to leave out the Midwest. The Cubs, Cards, Browns, Tigers, White Sox have had a great history, with some wonderful players, but they don't have the sparkle of East Coast players.
Let us look at the World Series Winners. From 1903 to 1970 there were about 20 winners from the Midwest (Chicago, St. Louis, Detroit, Cincinnati and Cleveland). Three winners from the West Coast (LA Dodgers). The remaining (approximately 45) series were won by East Coast teams.
I think that the auction houses cater towards older collectors. And who do they collect? Their boyhood heroes.
The players that played for their favorite teams.
The teams that are based on the East Coast.
So, yes, there is an ECS. But not by design. By history.