I agree. I am an Architectural Technologist and work on large scale residential developments for national housebuilder clients. In my 28 year career, I have only dealt with one development of apartments in which a sprinkler system was installed (at the time, the late 90's it was the first development in Surrey to include one). The only reason it was included was because it was the only way to achieve Building Regulation compliance for the design.
You have to remember that the Building Regulations set out the MINIMUM standards that buildings must be constructed to. Most developers see that as the benchmark and anything else is "guilding the lily". The current Part B documents do include references to sprinklers however they only come into play if certain other criteria cannot be met - more often than not, you can make a building safe from fire spread by applying the minimum standards.
There is also no requirement to install a communal fire alarm system - only smoke/heat detectors within individual flats - and 'stay put' policy is normal.
Most tower blocks being designed these days will include the services of a Fire Engineering Consultant to ensure that the design of a building not only complies with the regulations, but exceeds them - sometimes professional engineering not only provides a compliant solution, but can represent a saving to the developer on a design that complies with the minimum standards.
My personal view is that we will see the Building Regulations updated to make sprinkler systems mandatory. Unfortunately, it has taken a catastrophic & tragic event such as this to start the process.
Sprinklers are mandatory in buildings over 30m in height, roughly speaking this means anything with ground plus 10 floors. However this relatively recent and there is no requirement to retrospectively fit sprinklers to existing buildings over 30m in height.