A bit like the M25... a victim of its own success, which was designed to alleviate traffic congestion and provide better routing around London, its unexpected popularity soon led to congestion on itself.

I don't think BA really expected this offer would be as popular as it has turned out to be and didn't expect to extend it either - and, at a time when money was being lost all over the place and staff being furloughed/laid off, who would have put a proposal to the board about spending time and money on automating/computerising the whole process for a limited time offer (particularly when they know their own reputation for IT projects)?
Or even suggest taking staff off of the already swamped phone lines to manually process the qualifying holidays, let alone deal with the queries when things would go a little pear shaped?

They would be a brave person to propose these things at a time when everyone was being laid off or furloughed, I think!