Very good question!
Actually this goes back to the history of fluorescent lamp standardisation. Many decades ago it was desired by many manufacturers to have FL lamps in discrete colour temperature steps eg 2700, 3000, 3500, 4000, 4500, 6500K. Each manufacturer had their own unique phosphor composition to arrive at those values, which meant that the spectrum of one manufacturer’s lamp could be quite different than another even though their CCT’s were identical. As such, their chromaticity appearances and colour rendering indices could also differ. This was especially troublesome in large installations when replacing failed lamps of one brand by another : the differences were visually undesirable.
The lampmakers then began to standardise on the same phosphor recipes for each lamp colour, and the situation was greatly improved. Later still, it was discovered that actually it was not efficient to target numerically precise colour temperatures. For instance, by shifting from 4000K to 4100K it was possible to achieve a considerable cost saving in the raw phosphors, along with higher luminous efficacy, often a better colour rendering, and sometimes also better life. There were large-scale collaborative efforts among the world’s principal lampmakers, co-ordinated via the standardising committees of the IEC and ANSI, to work out a set of optimal chromaticity points for FL lamps that would allow manufacturers to make better and lower cost lamps with improved interchangeability between brands. These target chromaticities are specified in the relevant international standards and while they are not compulsory, it is highly recommended that manufacturers adhere to these.
When LEDs began to become popular for general lighting, both the ANSI and IEC performance standards encouraged nanufacturers to follow the same chromaticities and CCT’s as had been long established for fluorescent lamps. This position was strongly supported by the traditional lampmakers and fixture manufacturers, so as to make the transition from traditional to LED lighting as seamless as possible. However, the LED emitter manufacturers did not agree, for the very good reason that just like the performance and cost of FL lamps can be improved by targetting certain colour points, exactly the same is true for the available LED phosphors. As such, led by the USA LED manufacturers which were formerly the leaders of that industry, ANSI standardised a different set of colour points. Those have in the mean time been adopted almost worldwide. The IEC LED performance standard continues to state that it is desirable to make LED products with same chromaticities as the old standardised F-series colour points, which is a bit silly because I think nobody actually does that any more. Indeed, LED phosphors are also now developing at such terrific rate that even the ANSI LED colour points of the early 2000s are no longer always being followed.
