Artists aren’t charging more for concerts because they are making less money on album sales. Concert tickets are priced based on supply and demand. If they could have been charging $750 back then, they would have, no matter how much they were making on album sales.

I do think you might be right, though, that there is a causal relationship between diminished album revenue and more expensive tickets, it just isn’t because the artists need the money. Since most people can now listen to all the music they want for a flat fee, music lovers can now spend more of their hobby money on concert tickets, which increases price very directly since supply is limited.