I have given up on all strategies for getting subscribers and have gone the sales man route so when like i am travelling using a public transport i spot someone using a cell phone with data on i tell them to please subscribe and hand them over a toffee; at my work place i put my mobile hot spot on and tell every one to use my data and subscribe to my channel. I give real life cta for getting subscribers and trust me i got 16 subscribers using this method just today so this method is working. Thing with getting youtube subscribers is you need to ask alot and to be frank during the video CTA is a huge issue for me but i think i need to start doing this more often if i were to reach my goal of 100k subscribers by the end of 2030.
The real problem with is are they actually watching your videos? If not, then what you really have is a content problem.