It will lift up just a little bit (like a couple of inches), and then it will just stop. The motors stop spinning and the lift just stays at the same height.
Try using a bigger gear ratio. You can look up compound gear ratios because that is what you need. You might want to put the gears inside of the frame (on the lift and drive) otherwise the gears might slip. Also please add some bearings and improve your build quality. It might be helpful to design your robot in CAD and then build it, otherwise it might be sketchy. I really hope this helps.
Usually, if you are using more than 2-3 green gears on each side of your lift then you are likely wasting your precious time and energy. That is way too many gears, you should only be doing what is necessary.
There may be alot of built up pressure/friction because the gears are on the outside without any other c-channel on the outside. It may also help if there were bearings blocks so that the axles are not rubbing against the c-channel.
Your motors probably don’t have the power to lift up all the way. As everyone else said, use bearings/pillow blocks and reduce how many gears you are using. Another tip though is to add some rubber bands so the lift can just pseudo float and there is less load on the motors. You can also try and use a different gear ratio (motor core).
Like everyone has said bearing flats, also washers to give clearance to the C-channels. I would go with the 12T high strength but if you dont have it use the other thin 12T looking one and put 2 together on the drive shaft