I think the suggestion was there were only 3 tables open as there were not enough tables for a 4th.
If not, then there can often still be an issue

Lets say table 1 is 2/4 limit and full, table 2 is 4/8 limit with 7 players, table 3 is no limit and full and there is a waitlist of 3 players for no limit.
Poker room opens a 4th table for no-limit - the 3 players sit down, 3 players join from the 2/4 and 3 join from the 4/8
The table 2 now only has 4 players and closes. The table 1 only has 6 tables and could well close shortly.

Opening a 4th table could result in the closing of two existing ones.