how platforms like TIGR make money

Not a market maker, intermediary platforms like $Tiger Brokers(TIGR)$ depend heavily on their customer base. 

The peak in its profitability is achieved only when it is newly launched. There will only be newer and better platforms. 

Eventually, as 'wear and tear occurs', TIGR will see diminishing profits. This may push the platform to sell consumer and even trading data to major firms as a form of side income. It could even go as far as introducing slippage, and more to enhance its own profitability. This statement may or may not be true but things like network speed could play a part. It Is very logical for a platform to do so. As time passes, users may catch on with the quirks of a platform and lose trust in it, prompting them towards other major power aligned platforms.