Lion and Tiger exposed battlecruiser cost growth before Hood

Why did Lion and Tiger reveal that battlecruisers were becoming too expensive rather than Hood?

Because Lion and Tiger were the first sharp price jump over armoured cruisers; Hood was a later wartime escalation of a trend already apparent.

Invincible did not represent a dramatic cost break from the armoured cruisers that preceded her. Lion and Tiger did, making the new financial trend visible before Hood was laid down. Hood's much larger bill confirmed and accelerated that growth. Wartime construction also weakened ordinary cost controls, so her price was a later escalation rather than the first warning.