The load factor on the FRA did appear to improve after LH announced withdrawal.
I know companies, including airlines, can change their minds but I do remember the quote from the LH UK rep at the time they said they were pulling out, albeit there was some ambiguity as to whether it was a permanent move.
She said it was unlikely that things would change in 2010 to permit a return of the service.
Although the loads may have been improving they may still have been less than LH needed to ensure a yield that would sustain the route, albeit fares were often sky high as I'm sure Bristol_Traveller would confirm.
During its 13 months of operation the LH BRS-FRA route carried 99,000 passengers which at least shows there is a market. LH had a lot of passengers feeding into its long haul network - by the end of the first six months of operation passengers from BRS had flown to every worldwide LH destination - and it is unlikely that any other airline flying BRS-FRA would have that sort of advantage.
When one considers that BRS has sixteen French routes operated by Air France, easyJet and Ryanair between them Germany does look bare.
Apart from easyJet to Berlin there is only the niche OLT route to Bremen.