You don't necessarily want all batteries to come with built in protection. Today, you have the option of with or without.
Each protection circuit comes with a power cost. Consider the most basic protection: a resettable fuse (real protection circuitry is more complex).
If you put a resettable fuse on every battery in a pack that tiny voltage drop across a single battery will occur across each and every battery in your pack.
A small number of batteries and you wouldn't notice. But if you're looking at hundreds or thousands of cells it gets to be a major issue. Looking at string of batteries in series, if you draw a large current from the pack you'd find your pack voltage drops and you generate a lot of useless heat.
When building custom packs beyond hobbyist stuff it's often better to source (or design) your own battery management system than to rely on safety circuitry in each cell.
And that's not even mentioning the pack management and communications capabilities that custom pack- or string- based management circuitry would have.
Each protection circuit comes with a power cost. Consider the most basic protection: a resettable fuse (real protection circuitry is more complex).
If you put a resettable fuse on every battery in a pack that tiny voltage drop across a single battery will occur across each and every battery in your pack.
A small number of batteries and you wouldn't notice. But if you're looking at hundreds or thousands of cells it gets to be a major issue. Looking at string of batteries in series, if you draw a large current from the pack you'd find your pack voltage drops and you generate a lot of useless heat.
When building custom packs beyond hobbyist stuff it's often better to source (or design) your own battery management system than to rely on safety circuitry in each cell.
And that's not even mentioning the pack management and communications capabilities that custom pack- or string- based management circuitry would have.