Not sure it was only that. I remember a lot of "we're not Java" in the discussions around it. I always had the feeling, they were rejecting certain ideas like exceptions and generics more out of principle, than any practical analysis.
Like, yes, those ideas have frequently been driven too far and have led to their own pain points. But people also seem to frequently rediscover that removing them entirety will lead to pain, too.
I feel especially with generics though, there is a sort of loop that many languages fall into. It goes something like this:
(1) "Generics are too complicated and academical and in the real world we only need them for a small number of well-known tasks anyway, so let's just leave them out!"
(2) The amount of code that does need generics but now has to work around the lack of them piles up, leading to an explosion of different libraries, design patterns, etc, that all try to partially recreate them in their own way.
(3) The language designers finally cave and introduce some kind of generics support in a later version of the language. However, at this point, they have to deal with all the "legacy" code that is not generics-aware and with runtime environments that aren't either. It also somehow has to play nice with all the ad-hoc solutions that are still present. So the new implementation has to deal with a myriad of special cases and tradeoffs that wouldn't be there in the first if it had been included in the language from the beginning.
(4) All the tradeoffs give the feature a reputation of needless complexity and frustrating limitations and/or footguns, prompting the next language designer to wonder if they should include them at all. Go to (1) ...
Ian Lance Taylor, a big proponent of generics, wrote a lot about the difficulties of adding generics to Golang. I bet the initial team just had to cut the scope and produce a working language, as simple as possible while still practically useful. Easy concurrency was the goal, so they basically took mostl of Modula-2 plus ideas form Oberon (and elsewhere), removed all the "fluff" (like arrays indexable by enumeration types, etc), added GC, and that was plenty enough.