1) They already chain down all the tools and/or keep them boxed without store displays such that it is very difficult to evaluate tools you might wish to purchase. You can't even pick them up to get a feeling for the weight. Many of the more robust tools (table saws, drill presses, etc) they don't keep in stock either.
2) So many of the accidental thefts in the comments are due to self-scanning. Well - why were consumers forced to self-checkout in the first place? Because HD never has enough checkers, their checkout areas are poorly designed for the kinds of bulk items being purchased, and basically HD is being cheap and wants to lower their costs by putting the burden back on the consumer. Sure, I do my best to scan accurately and ethically, but I can completely see how this happens and it is difficult to blame the consumer when HD has deliberately funnel you into self-checkout.