Simple example if you use wildcard exclusions your build will fail because it's available only with maven 3.3.3 and the current embedder will reject the pom as a failure whereas it's not.
This plugin has some technical constraints (defaults..) so it's impossible to manage such legacy builds and upgrade for new features and/or security reasons.
BTW we are now in 2019j jdk6 and jdk7 are definitely EOL/DEAD
one day we have to stop trying to maintain those very old/legacy...
If it's a big issue for you you can definitely use freestyle or pipeline plugins, use maven toolchain, configure compiler target/source attributes, animal-sniffer plugin.... few options.
Fully agree on dropping maven2 support as EOL, but raising minimal version requires justification. Many large enterprises have large legacy codebases built on maven 3.1.1 (and JDK 6).
An arbitrary change to minimal version will have negative impacts across many plugins, effectively freezing our installed Jenkins configuration.
I hear the "buts" - using jdk 6 and M3.1.1 also has repercussions, but is there a justifiable reason to raise the minimal version ?