I did not understand that sentence.

The way I see it, customer buys a vote from the bot, bot gets the fee as a liquid payment, passes it on to the delegators who will often, though not always, sell it as a source of passive income. (It is certainly possible in an individual case that they aren't selling and are accumulating Steem, but if that were happening on a broad scale, we'd see a very different Steem price.)