When I started watching DW - first episode ever! - sci fi was a slightly outlandish genre. Not too many people were that into it, so questions like ageing in different time lines didn't really come up so much; also it was primarily for kids. People didn't worry about realism so much either, not for programmes which were clearly fantasy, just suspended disbelief as far as was required, and ignored stuff like that.
50 years later, sci fi and fantasy are old established genres. We all know what sort of questions to ask, how to find anomalies, we question everything. In DW's early years, there were plenty of paradoxes, things which didn't add up, things which didn't make sense, things which were simply forgotten about. No one minded, it was all fun and frightening, and exciting (for us kids anyway, my parents thought it was enjoyable tosh).
It also is much less of a programme for children now and much more for their mums.
And I shall be very sorry indeed to see Amy go next week, but I'll let you all be horrid about it (sob) if you like as I've seen sooooo many companions go and I can't remember half of them. I think I had a small crush on Frazier Hines during his time, but once he'd gone I don't think I thought about him again until now.