By numbers of communication actions, pretty much everything may actually be a message exchange, but by the amount of data that was transferred for many years the file downloads and uploads had been dominant on the Internet, which are the kind of thing for which TCP has been designed. For a big file more data may be transferred than for thousands or millions of message exchanges.

Nowadays perhaps video streaming, which may be lossy, so TCP is not needed for it (i.e. what is now called streaming does not have the reliability requirements of the TCP streams), might transfer more data on the Internet than file downloads, but that is not a desirable technical evolution, the replacement of downloading with streaming is just a means to extract more money from those who are satisfied by such a service.