Older Cell / Smart phones were susceptible to bluesnarfing / bluetooth attacks, Why specifically are smartphones secure from this attack now?

Older cell / smart phones were susceptible to bluesnarfing / Bluetooth attacks, Nokia phones in particular. But now in days, modern smart phone and cell phones that use Bluetooth technology for pairing, which made phones vulnerable to various types of Bluetooth attacks, are no longer able to be attacked with the same tools and technology that they were able to be hacked in the past.

Why ?? What specifically has been changed about the Bluetooth technology in modern phones, that keeps them safe ?

I've used Kali Linux Bluetooth technology and I am not able to bluesnarf attack my own devices for some reason. This is a good thing for security, but I need to understand what changed.