Why is it? It is standard consultation. Submitting a planning application costs money as does the work being proposed so it is only sensible that an applicant takes advice to ensure they aren't submitting something that has absolutely no chance of success.

The planning system is not supposed to be subjective so an applicant should expect to be successful if they adhere to the relevant parts and plans of the Town and Country Planning system and local authority. Where the application does not fall in a Conservation Area or affect a listed buiding (directly or indirectly) the proposal for a different architectural style should not be used in an 'out-of-character' argument in an objection/refusal. The 'out-of-character' objection should only be applied to things like land-use type, scale of buildings, building line, overly dense population.

Significant structural work on existing, older buildings has the potential to be far more expensive than a new-build, which is possibly why the applicant is proposing a new build.

Subsidence is often covered by insurance but it is wrong to assume that the property was covered by buildings insurance - there are many reasons why it might not be covered. Unless it has been sold in the last couple of months, open source information suggests 139 hasn't changed hands in (at least) the last 8 years. Imagine you are told you have ?200,000 worth of repairs that need doing to your house and, for whatever reason, you are liable for the full cost as neither your insurance or local grants are in a position to contribute. Would you add that money to your mortgage (presuming the banks deemed you financially sound enough) just to retain a standard victorian house? It is more than possible that this person cannot afford to do this (or new-build a house for themselves) and the development opportunity on the site would allow them to return it to residential use and allow them to buy themselves somewhere to live again.

I dont want to see every house in Forest Hill replaced by flats but neither do I think that all apartment blocks should be built in the same place, just because there is a precedent. 11 flats might seem a lot but it seems to meet the required residential density and 125-129 Sunderland Road has 11 flats on a similar sized (but different shaped) site.