One of the reasons is that Complex Metamorphosis hadn't evolved yet. Lots of insects hatch from eggs as tiny versions of what they will eventually become. Being that they have their skeleton on the outside (exoskeleton) that doesn't grow by cell division, but rather splits open when outgrown to reveal another shell inside that the insect then grows into (and often out grows several time during their development (called Instars). Higher forms of insects change , metamorphosis) through dramatically different stages, like the difference between a caterpillar and a butterfly, accomplished during a pupal stage wherein the entire mass of the insect beaks down and rearranges to emerge as what appears to be an entirely different insect.
Another reason for the later appearance of insects that depend upon flowers (pollen or nectar)for food is that flowering plants had also hadn't evolved yet.
Like you (and any normal human being) "BUGZ" gave me the heebie-jeebies too, to the point where I couldn't bring myself to even touch the pages of books that were covered by pictures of insects... I used to grab the page by the extreme corner and flip it over (hoping there weren't more on the next page! )
I didn't get used to insects until working in the County Gardening Hot-Line Office... where people would always be handing me insects (both dead and alive) for me to identify, and instruct them upon HOW-TO kill the lil' buggers.
One reason I didn't like them was because I thought they'd BREAK as soon as I touched them, and all this ickie green stuff would come oozing out!
Turns out that they're far more robust than one would imaging ...given their size, and could withstand a good deal of handling...
Wait.. Ah.. now I remember... MY HUSBAND (r.i.p.) was an science buff (later to become a chemistry professor 'til the day he died) anyway, he had a childhood interest in entomology, and was forever grabbing bugs to examine... then he'd inevitably tell me to, "Hold out your hand" "NO!!!!" and he'd always say the same thing.. "Go ahead, let it walk onto your hand... it couldn't hurt you even if it wanted to."
So yeah, it took a bit of exposure, but I got used to it. lol NEVER thought I'd be allowing caterpillars to walk all over me while I cleaned their enclosures, let alone foraging for their food plants and feeding them several times a day for weeks at a time.