A slash might have another meaning; it could separate more than one word, for example, or be part of some technical term. A quick check of the first few entries in PLC shows me references to 4/4 time, an example "ground floor (UK) / first floor (US)", various velocities in km/s, a reference to A/H1N1 flu, camera f-stops, a list of the BRICS countries where simply looking for /s between words would leave you thinking that "Russia Africa" and "China Africa" were countries, etc.
These aren't unfixable problems, and one could probably come up with heuristics to catch a good % of them, but there'd still be a ton of proofreading and hand-checking involved - you really wouldn't want to do it wrong or you'd end up wrecking a lot of other searches that currently work fine - and I honestly don't know if enough people would benefit from this feature for it to be worth the effort.