Monitor mode is active, but no handshake are being captured.

[All3xJ]

I edited CONFIG_WIFI_MONITOR flag to make it support monitor mode.

Then I did:

sudo iwconfig wlp3s0f3u3 mode monitor
sudo airodump-ng wlp3s0f3u3

and the card is in monitor mode as you can see:

wlp3s0f3u3  IEEE 802.11b  ESSID:""  Nickname:"<WIFI@REALTEK>"
          Mode:Monitor  Frequency:2.412 GHz  Access Point: Not-Associated   
          Sensitivity:0/0  
          Retry:off   RTS thr:off   Fragment thr:off
          Power Management:off
          Link Quality:0  Signal level:0  Noise level:0
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0

but no handshakes are captured with airodump-ng... why?