Question regarding pending aircraft retirements
 

I was wondering if someone can explain to me why bolkows and sometime later, s61ns are being phased out and off the register? Is it a CAA instruction and why. Is it to do with them being more difficult to maintain/upgrade or what?
Are they inherently more unsafe than current replacements? There must be soem aircraft with relatively low airframe hours and it seems a terrible waste.
I'd appreciate any opinions or information.