At the Aldi in my area many of the token mechanism are broken, so the carts are always loose. They get put back by people anyways, which makes me happy.

Same in Austria. Noticed our Lidl removed the coin/token slot recently.

If the supermarket starts spending more on labour/lost carts than they were losing with lost business/upfront cost, they may bring them back.

I wonder what the conversation is between supermarkets. They have to know the one spending upfront for these devices is training the local population reducing the other's running costs.

I'm in Germany too, nobody leaves their trolleys sitting around.

That sucks. I noticed our Lidl did the same (maybe other supermarkets, too, haven't paid attention), but people still return the carts. This is in Austria. 

I think most of the trolley collectors are disabled in some way, so their jobs will be subsidised.

A bit beyond the scope of the post. But instead of supermarkets using society to subsidise their labour costs, we could use supermarkets to subsidise society. Tax the wealth and institute a UBI.

Absolutely true, it does present a barrier. I had a token attached to my keys for my own sanity.

Now that token perminantly lives in my car after the clippy thing broke. If I'm shopping for enough things to need a trolley, I have my car. My peers all have these things in the cupholder/ashtray of their center console.

The timing worked out, I had the token attached to my keys while I was without a car, and it broke just in time for the arrival of the car.