If you look at the list of U.S. Metropolitan Statistical Areas - i.e. the list of largest cities taking into account suburbs and not stopping at city limits - this is what you find.
The largest cities without an MLS francise are:
7 - Miami, 6.2 million
11 - Phoenix, 4.7 million
14 - Detroit, 4.3 million
17 - San Diego, 3.3 million
18 - Tampa, 3.1 million
20 - Baltimore, 2.8 million
21 - St. Louis, 2.8 million
22 - Charlotte, 2.5 million
24 - San Antonio, 2.5 million
Cities smaller than those with MLS Franchises:
25 - Portland, 2.5 million
29 - Cincinnatti, 2.2 million
30 - Kansas City, 2.1 million
32 - Columbus, 2.1 million (Austin, 2.1 million)
35 - San Jose, 2.0 million
48 - Salt Lake City, 1.2 million
The largest cities without an MLS francise are:
7 - Miami, 6.2 million
11 - Phoenix, 4.7 million
14 - Detroit, 4.3 million
17 - San Diego, 3.3 million
18 - Tampa, 3.1 million
20 - Baltimore, 2.8 million
21 - St. Louis, 2.8 million
22 - Charlotte, 2.5 million
24 - San Antonio, 2.5 million
Cities smaller than those with MLS Franchises:
25 - Portland, 2.5 million
29 - Cincinnatti, 2.2 million
30 - Kansas City, 2.1 million
32 - Columbus, 2.1 million (Austin, 2.1 million)
35 - San Jose, 2.0 million
48 - Salt Lake City, 1.2 million