It stayed at v5.1 (with some v5.2 features that don't break 5.1 code) because Mike Pall disagreed with some v5.2 features: swapping `setfenv` for `_ENV`, and some details of the bundled bitlib.
He also criticized 128 bits interpreter values mandated by the support of 64 bits integer in v5.3. These take twice as much cache space and damage performance.
He also criticized 128 bits interpreter values mandated by the support of 64 bits integer in v5.3. These take twice as much cache space and damage performance.