Just another symptom
With respect to the many excellent comments here, I think Maplin's death is being over-analysed: at risk of now over-simplifying, isn't it really the case that Maplin has followed many predecessor retailers into oblivion for basically similar reasons? Viz: fast delivering and significantly cheaper internet.
If we exclude grocery, and high street clothing stores—where, understandably, people still like to try stuff on—there isn't much left in bricks'n'mortar retail that internet suppliers cannot do more cheaply: simply because at scale, internet sellers can keep their overheads and costs lower. It's very hard to argue with the math of (a) no eyewateringly expensive high street rental and rates, (b) economies of scale through centralisation, and (c) industrial-grade tax avoidance.
Indeed, I'd go a little further and wonder why retailers like Boots and WHSmith are still infesting the high street. They are not good value, by and large, and do not, IMHO, have some specialised/USP offering that the 'net cannot compete with. (Why does anyone go into a WHS these days? I'm genuinely curious.)
I am one of those "mourning dads" that an early poster joked about, being of the speccy teen 70s generation that rescued old 405-line TVs off the pile behind the repair shop to take home and nurture back to life, and even now I still occasionally knock up a gadget (our house boiler was never meant to be connected to the Internet of Shyte) but, the arithmetic became very easy: Maplin couldn't be trusted to concentrate on what I really wanted, and if Amazon couldn't provide, Rapid could—thus the reasons even for walking in the door at Maplin simply evaporated over the years. (And that doesn't include avoiding the persistently eager staff, for I am, in my old age, of somewhat forbidding mien.)
Whether I am right or not about Boots and WHS, I claim no perspicacity for saying that Maplin won't be the last. If you are to survive in high street retail these days, you need to give customers an irresistibe reason to (a) walk in, and (b) walk out with something.