I'll just add my voice to the general grumbling. Gardening, like sport, is topical and needs to be shown at the right time, either live or very close to filming. A topical garden show will deal with the things we want to know now, this week, and will relate to the actual weather we're experiencing this year. Watching old repeats would be as much use as watching last year's Wimbledon.
Cutting out the only gardening show we have for a whole month during the height of summer is totally unreasonable. They set aside whole evenings for darts matches (who ever watches darts?), and hours at a stretch for golf, tennis, and of course football. If these events overrun, they're sacred and everything else gets squeezed out for them.
If there is another reason, the BBC are hiding it. What Monty said was that it was sporting events that had pushed GW out of the schedule. I feel a stiffly-worded complaint to the BBC or Radio Time coming on ...