The lending itself was profitable for them without them stealing from investors. The coin price is based on the demand for the coin which had a large community of people. Many didn't lend and just staked the coin as that normally paid quite a lot more than lending. If more people did lending, bitconnect would have been able to do more marketing with the extra profits.
Yes, the scheme was profitable for the scammers. They probably wouldn't have done it if they didn't expect profit. The demand for the coin was fueled solely by the ponzi scheme. There was no other use for the coin. Marketing or no marketing, every such scheme eventually collapses.