TCP packets of not all devices are captured ?

Hello all,

I'm a beginner at packet sniffing.I have been running wireshark on my Linux machine after enabling monitor mode for my wireless interface. I can only see TCP packets of very few devices being captured. I see a lot of 802.11 packets captured involving probe response/request information.

I am not able to understand why the TCP packets of the rest of the devices are not being captured. Is this because of the secure connection they all are connected to ? I would be glad if someone could throw some light on this.

Thanks in advance.