I have it on good authority from an original design team member that the LS3/5A was designed to emphasise distortion and HISSS in an outside broadcast van, nothing more as
@sergeauckland correctly suggests above - edit - they did find their way into the broadcast studios as a general sound-box before being replaces as below. It's NOT accurate on speech, the original brightness and later mid 80s screech saw to that and the 120Hz 'thump' was designed in to make them sound at least acceptable (the popular-used JR149 cylinders lacked this thump and simply sounded thin and somewhat tinny I remember). The 11 ohm revisions helped a bit, but I remember one afternoon at the Harbeth factory in 1990 or so, their 3/5A version (meticulously calibrated) was beaten handsomely in imagery and top-bottom seamlessness by the original Harbeth P3 model, itself subsequently hugely developed into the current P3ESR-XD models thirty five odd years on...
We sold LS3/5As (Rogers, Chartwell and Audiomaster) to those who wanted a dinky box with a bigger sound, the BBC monika on the back an added bonus. Nobody made any money from them I remember, as the B110 drive unit varied a lot even in the borderline spec required for the design and so much fiddling in the crossovers was needed to get each one to conform (first hand experience of failed batches being hand-tuned to bring them into line), that's assuming the makers bothered. The baby Spendor SA1 wasn't especially a competitor as it was slightly chunkier, but when new, what a delightful tone it had - HiFi Choice suggesting it came into its own with digital sources (I'd moved jobs to a non-Spendor dealership by then)
All ancient history now and samples of these boxes sell for silly-high amounts to collectors, as do vintage Tannoys and similar. new Falcon ones I heard immediately reminded mne why I loathe this speaker today, all screech and tinsssssel up top, but the demming dealer thought this is 'detail' so there you are...
As for the BBC, they 'upgraded' to Dynaudio actives (BM5As I think) in their studio refits a couple of decades or more back, so that's where afficionado interests should look.
I gave up two thirds into the list, but what in the UK about the Spendor BC1, KEF 104ab and especially R105, along with the B&W 801 and I think the 802 and 805, which found itself placed in so mastering studios (Polygram especially in the 80s and 90s), the N800s regularly seen today, doorstops or otherwise