There’s also a difference in German signalling system architecture which made resignalling with electric / electronic systems rather more expensive than over here.
Until recently, all new German electric signalling had to be hard wired back to the interlocking. That means a LOT of cables. (Over here we often use vital telecoms links between signalboxes / interlockings / ground equipment - exchanging what would be hundreds of signalling & power cables for a pair of comms cables).
Hence the economics of resignalling was perhaps not as attractive as over here.
Up until the early 2000s that was all that was on offer from Siemens, the main signalling supplier in West Germany, and under Railtrack/early NR, the UK purchased a small number of installations based on the same technology, for Bournemouth and Portsmouth resignalling. In terms of cabling, the Siemens 'SIMIS' processor-based product line was little different to 1960s and 70s era UK relay-based signalling with large remote equipment rooms each covering a major junction or station and every trackside function hardwired directly from the input/output stages in those rooms. Starting with SSI in the 1980s, BR processor-based systems could be engineered with a far more distributed input/output architecture housed in smaller cabinets located much closer to the controlled trackside objects, linked by trackside datalink cables instead and requiring far less cabling in total than previous relay-based solutions and the contemporary Siemens offering. Sometime after the rather unsuccessful Portsmouth project, Siemens lost their framework contracts for UK signalling renewals using the German technology, but later successfully re-entered the UK market by acquiring the former Westinghouse signalling businesses and product lines from Invensys, and were then able to offer SSI-based solutions and much local UK legacy project expertise. They also updated their German products to offer a more distributed input/output paradigm.
While this concern may have some bearing on the early digital era from the 1980s, it doesn't really explain why more centralised electrical signalling wasn't provided in Germany in the 1960s and 70s, when there was little difference conceptually between the relay-based solutions available in Germany and UK, although it is interesting to note that the UK, while on the one hand having some of the most centralised signalling control installations anywhere in Europe today, simultaneously also retains some of the smallest signal box control areas as well, mostly in rural areas clearly! There are even some sizable mechanical installations remaining on main lines, albeit not always with semaphores. While most people know about Shrewsbury and Worcester due to their obvious semaphores, few realise the Stockport area colour lights are still operated from a series of mechanical lever boxes. Stafford was until recently also mechanically controlled colour lights. Both of these areas were legacies of repeated WCML modernisation programmes running into problems!