Updated Press Release on NOM of the Convening Shareholders, page-40

It is the usual story really, people do not provide free services. There is always a catch somewhere so that they can make money.
i cannot see them making money out of providing a voting "capability" for individuals because they have to carry out clerical activity to record the votes of individual participants in the IBKR holding which are then aggregated and applied accordingly against the single IBKR holding.
IBKR make their real money by "lending out" the shares or other such activity. Maybe they short and cover with their clients holdings. Provided they can make good when a client sells then they can get away with this but I was not prepared to risk my shares like this, regardless of the low brokerage cost. I have seen a number of brokers go broke over the years.