Retailers in wealthier areas have larger budgets, higher profit margins, and more attention by the executives. The favorite managers get assigned to the better stores and regions because obviously it involves better bonuses and better quality of life. They then invest in bullshit security upgrades because they can, and the C-suite believes they work because, well, the managers saying they work were already the favorites.

Retailers in lower income neighborhoods literally can't afford long-term investments - corporate runs them on razor-thin margins, assigns them the worst managers by default and doesn't trust those managers, and underpays their staff such that they're constantly dealing with turnover.

Even if they found the temporary budget to install the security measures, they would still need a permanent budget to maintain them, and it still wouldn't be worth it because:

1. if $X worth of shopping carts walk out the door, and you add $Y worth of security measures... now $X+$Y are walking out the door.
2. if shopping carts are constantly locking up and malfunctioning due to underfunded maintenance, $Z worth of shopping carts are now sitting in the store doing nothing, which in the corporate world is almost as bad as that money walking out the door.