In NR SCS, why do we have extended CP only in 60 kHz?

Hello Experts,
5G NR supports multiple OFDM Sub-Carrier Spacing (SCS)
15, 30, 60, 120 and 240 kHz is supported.

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Why do we have extended CP only in 60 kHz?
Any reason behind this?

Extended CP is for cells with large delay spread, but don’t know why only for 60 KHz.