Legally, you're missing the finer details of what's going on.
Life normally has a set legal meaning (99 years in most places here in the States). So, a "life" sentence is a "99 year" sentence.
Then, you may get our early for time served, probation, good behavior, blah blah blah. But that all comes after the fact. They ARE sentenced to life, but mitigating factors are then applied that reduce the actual time served after the sentencing.
As an outside observer, we often only hear only the initial and the final calculations and not all the details and finer legal points that went on in-between to create the difference in the two.
It is no different than sentencing someone to 20 years and then letting them out after 12 for whatever reason. Should we change EVERY legal sentence to mean exactly what it initially states and do away with reductions for any reason ever?
Or, to see the same effect in a wholly different context...
This is like saying to an employee "Your salary is $1000 per month!" But then you only pay them $682.17 because you take that original $1000 and subtract various state and federal income and social security taxes, health care, 401k contributions, etc, etc, etc. But *technically,* *legally* your base and reported salary is still $1000 per month, even if you only *receive* $682.17 per month in actualized monies.
Normally, if you want "life" to mean "life," then you sentence to "life without parole." Just "life" is understood to meant that there is a possibility of parole. This would be the equivalent of saying "pay" versus "pay without taxes."
We can talk about redefining life, but it already does come with a specific, clear, purposeful legal meaning most times. The meaning may seem disparate with reality to a layperson, but lay people aren't the ones in the courtrooms practicing law every day. To lawyers, the term "life" DOES carry a specific meaning that they can then work with.
This is a situation where I say we let the professionals who deal with it handle how their own profession defines a thing and recognize and admit that--as outside lay people--we not only shouldn't try to have a say, but we shouldn't think we know better than they do about a thing we understand less about.
(I'm not a lawyer, but I work in a profession in which outsiders are constantly wanting to redefine our workflows and terminologies to things they could understand easier, but that would make our jobs harder and less efficient.)