They're not being offered more goodies, just to remain under the existing terms. The ongoing negotiations are about the terms if they do leave, where there will certainly be a net loss of goodies.
Except they have already lost two major European agencies (European Medicines Agency and European Banking Authority) that are being relocated to Amsterdam and Paris.
[1] https://www.consilium.europa.eu/en/press/press-releases/2018...
This is a proposal for relocation if Brexit goes ahead. If it doesn't go ahead, there's no point relocating.