I'm also aware many of those places have either refused to relinquish space, or have done so but have no more to give back. Quoting Doug Barton, former manager at IANA, July 2015: "... Many orgs did give back space and/or swap allocations. But that well ran dry long ago" (if you need a reference link for that quote, let me know).
A recent example of relinquishing space is 18.0.0.0/8 (previously MIT) as of April 2017, which now has many /16 and /24 segments delegated to companies such as Comcast (ex. 18.10.0.0/16), Amazon (ex. 18.145.0.0/16), and Akamai (ex. 18.255.255.0/24), while many larger portions still reside with MIT (ex. 18.128.0.0/12, 18.0.0.0/9, 18.144.0.0/16).
My point of giving examples: note all the /16s. If you need further examples, refer to IANA's Recovered Address Space document and note the subnet sizes (many are much smaller than a /16): https://www.iana.org/assignments/ipv4-recovered-address-spac...
Every little bit counts.
While this may be a lot for typical users, it's not huge for a large IT company. You know that HP has 2 /8s, right?