The relocation is basically about BBC budget cuts and modernizing production infrastructure. They've consolidated a bunch of their drama recording into MediaCityUK up in Salford, which is where a lot of their other output happens now anyway. It's cheaper to have everything in one place rather than maintaining separate facilities in Birmingham - fewer overhead costs, easier to share equipment and staff across shows.
From a fan perspective it's a bit sad because yeah, it's a massive part of the show's identity that it was rooted in the Midlands for so long. But honestly the actual production quality shouldn't suffer much - if anything they might have access to better tech and studios at MediaCityUK. The real issue is more the symbolic thing, losing that Birmingham connection that made the show feel genuinely tied to a specific place. The scripts and performances will still be about Ambridge and rural life, but it loses some authenticity when it's being made somewhere completely different.
The previous answer's dates are a bit off though - The Archers has been running since 1951, so we're well past 75 years now. Still, the move itself happened relatively recently and it was definitely a significant shift after all that time in one location.