IAB only has about 128 bill of client assets while TD Ameritrade has 1.3 Trillion and Schwab has 3.3 Trillion.
IAB's changes are probably reacting to the volatility increases , especially in small caps. Last week alone 120 companies in the S&P 600 small cap index lost 20% of their value. And IAB attracts gamblers as its margin loan rates are only about 20% of the rates charged by Schwab and TD Ameritrade. eg for a $300,000 margin account loan IAB's rate is 1.41% while Schwab is 7.57% and TD is 8.25%.
The changes also affected longs for companies above 5 bill market cap.