Well first only about 1% of all companies current use
SEO services.
While I'm not sure of stats in the USA, in Canada there are 936,000 registered businesses, about 65% are considered "small" and about 33% are medium that leaves about 2% at large...
The USA cannot be too far off that... so why worry about 2% when only 1% of the other (likely) 98% are not being serviced.