They have been stopping a lot more of them over at least the last six months or year. I think we are just shown a lot of the ones that do make it through by media that wants to make sure that Ukraine looks like they are doing better than they are. Much like the "Iron Dome", if enough are sent over, plenty will eventually hit the target. With all the drones having cameras, they will have great footage of the ones that make it to their targets, and can play those on repeat for media and social media. A numbers game, they are able to send a fuckton of cheap converted consumer models.

You don't inspire hope and support by showing the L's. Just like how Israel is making sure to downplay their own loses. And of course making sure to buy off support from for-profit media and politicians that matter. That way the narrative is kept as being "innocent and pure of heart Israel is just protecting themselves" and that Iran is being the "aggressor by their unprovoked missile and drone strikes". While completely acting like Israel didn't blow up the Iranian embassy first. Or how Israel is actively bombing other nations on a daily basis.

Russia can’t stop the drones

Except they do. Ukraine and western media are publishing and riding hard every sussessful attack, but you never heard about the unuccessful ones because just think for a second, why they would tell everyone about failures. But just consider number of drones and missiles Ukraine is said to operate, and you would immediately notice they are either not using them or they do use it and fail most of the time.

If you send 100 drones and give me a machine gun I may be able to shoot a few down. You give me one these and maybe I can shoot down 90 of them. What would you prefer? Letting 10 through or letting 95 through?