I’ve read that many contracts involved the label fronting a ton of money to the band to produce and promote the album.

Which meant the band needed to tour to generate the revenue and exposure to pay all that money back. Shirts and posters cost nothing to print and sell for $35 at the table. Exclusive tour merch is collectible.

Streaming and digital production changed this somewhat but the economy seems similar today. Since nobody buys albums and streaming pays nothing, tours and merch are where the band gets paid.

Today perhaps. But in the past the artists money from selling records. So the tour was to promote the album, rather than the other way around