It's a skilled job, fattening an entire ram lamb. At a certain age/stage, they can lose interest in feeding as other things begin to take their attention. The butcher then can be presented with a rather poor carcase, and it costs him the same to butcher it as a fully-fleshed one, but he will get a lot less back in sales.
Our butcher will take any lamb from us, because he trusts us to know what he wants. But at a certain point in the season, if we send him more than the odd entire ram lamb, he will quietly mention that we "seem to be getting the tail-enders now," and that perhaps he won't have any more after the current batch...

In truth, it's a skilled job, fattening
any lamb for a High St or village butcher. Too fat and it costs him more to butcher it as he has to do a lot of trimming, plus he's paid for it per kilo deadweight and has to throw a lot of fat away; too little flesh and/or poor conformation, and his cost to butcher per kilo goes up. Too young and there may be insufficient flavour; too much cake and the texture may suffer; too slow-grown and the fat may be yellow which some buyers won't like, and so on.