As Lyn Alden points out, these cash limits are almost never indexed to inflation. Hence, they become more restrictive over time (https://twitter.com/lynaldencontact/status/15537499345743708...):

… the US Bank Secrecy Act of 1970 made banks file gov reports on transactions/deposits over $10k (which was worth the equivalent of $80k today).

By never changing the threshold while dollars became worth 1/8th of what they used to, they broadened the scope by 8x.