Did you have older siblings esp with a big gap between them and you? This would be quite unusual in the 90s. In 1993 a law was passed to require all children under 3 to use a child seat, although it was still allowed for children aged 3+ to just use a seatbelt (or nothing, in the back, if one wasn't available).
OTOH I was born in the late 80s, so just short of this law, I don't remember using a child seat and only occasionally a booster seat when my grandad read an article about them and insisted on them, but we all thought he was being silly and overprotective. I know I did use a car seat as a toddler, because there's a picture of me in it, but it's before I can remember.
I don't know how much was made of this in the news etc, so it's possible if you had older siblings, your parents just did the same as they had for them, not realising the law had changed. The first ever UK law involving child seats was passed in 1989, but it was fairly pointless as it basically was only a problem if there was a child seat installed and the child in question wasn't in it. If you just didn't have one, it didn't matter.
1991 was when seatbelts had to be fitted in the back and front of all cars, I believe this included retrofitting, apart from classic cars over a certain age, but don't know the exact details any more. This would have made a big difference in the ability to fit child seats, because if you didn't have seatbelts in the back of your car, you had to bolt the seat to the seatbelt mounting point using special straps, so they couldn't easily be moved between vehicles or moved for an adult to sit there. I assume this is the reason that the law before 1993 was about using child seats only "when available" - because they were permanently installed.
I suspect we have a similar "blind spot" happening currently, because the law changed again in 2006, stating that children over 3 but under 12 or 135cm must continue to use a child seat or booster seat.
Anyone under 10/11 in 2006 (so, currently under 30) is likely to be aware of this rule, because they would remember it affecting them. So the "blind spot" will pass within the next 10-15 years as this cohort have primary school aged children.
Anyone working in the industry takes it for granted that it's obvious, because it's been the case for nearly 20 years.
But it's not obvious to someone who was already over 12 in 2006, ie, adults currently in their 30s/40s - it's much more likely that they don't remember a law change which happened 20 years ago when they themselves were in their teens or mid 20s and not thinking about children at all. They probably take it for granted that very young children need child seats, because these have been in common use throughout their entire lifetime, but the use among older children has not been consistent, and the publicity about the law change stopped years ago. Some people will look it up to be sure, but some people will simply make an assumption.
So you have quite a lot of parents of primary school aged children currently who automatically buy and use child seats for their babies and toddlers, but don't realise that they are required up to 12 years of age or 135cm, and stop using them early.