It is the "obviousness" of the fault that is the issue, more than the type of equipment - after all, we can probably all repair a scope with a blown fuse, on a good day!
replacing blown fuse in audio amp is a matter of pulling and replacing it from behind, no dismantling needed. i have Advantest SA here that has intermittent fault. when i opened it, it has 5 or 6 pcbs stacked on top of each other and on the side with countless rigid coax cable connections, countless number of power rails and each pcb is more than 2 layers stack technology probaly 4 or 6 layers (how to trace connection?) 3-10X smd components count and complexity, several mcus rams etc. i just dont know where to start, so i put back the cover in sadness, being afraid of making more damage than good. i need to learn SA diagram, there are lot of sections one must be familiar with every rf components, switches, attenuators, amplfiers etc what they do, i say... super difficult on grade 10. i guess will need hundreds or thousands of pages if someone want to hand guide me in a forum.
otoh with audio amp, its 2 layers pcb tech, through holes, super minimal smd count. i managed to create schematics of its major section and understand it in few hours or so less than a day from nothing. i'm not quite interested in audio filter and conditioning section they are seldomly got damaged, so i didnt make its schematics, although i have general picture of what they are, they are only few TH resistors, caps, resistors and caps again and small bjts thats it. audio amp is nothing but (1) step up smps providing higher power rail (usually one +ve and one -ve rail only) (2) audio filters and conditioning at input (seldomly damaged) (3) the audio power amplifier (those big bjts). its quite easy to understand. no, audio amp and a SA are not the same, they like earth and sky difference in complexity, unobviousness-wise and skill/knowledge level required. ymmv.