It's very hard to make "smart" bots. Can you list me few indie shooter games where it's interesting to play against bots? I personally never played any.
If you want to see more players in game, you can record some gameplay videos and upload on youtube. Or tell your friends about game and play with them. If at least 5% of player base would record some gameplay videos, online would be above 100. If you will search on youtube "skillwarz" you will see that in last 30 days only 1 gameplay video is uploaded. I have never seen so low number and it translates to number of players in game.
Online will be higher when game will move to Steam (planned Q2 2022).