I guess this will hit all electric vehicles at first. Due to the higher weight you will have more energetic collisions compared to fuel powered cars. Of course there are still differences by model.
https://cdn.euroncap.com/media/55749/euroncap-2019-tesla-mod...
BMW iX: 5 stars
https://cdn.euroncap.com/media/67239/euroncap-2021-bmw-ix-da...
Jaguar I-Pace: 5 stars
https://cdn.euroncap.com/media/63559/euroncap-2018-jaguar-i-...
Nissan Leaf: 5 stars
https://cdn.euroncap.com/media/62961/euroncap-2018-nissan-le...
VW ID3: 5 stars
https://cdn.euroncap.com/media/64338/euroncap-2020-vw-id3-da...
VW ID4: 5 stars
https://cdn.euroncap.com/media/64335/euroncap-2021-vw-id4-da...
Hyundai Ioniq 5: 5 stars
https://cdn.euroncap.com/media/67127/euroncap-2021-hyundai-i...
Ford Mustang Mach-e: 5 stars
https://cdn.euroncap.com/media/65695/euroncap-2021-ford-must...
Zoe is an urban supermini, only slightly bigger than a Smart or Twingo. And with minimal equipment (no expensive assistive systems) to bring the price down because otherwise it wouldn't be possible to sell it.
Zoe pricing starts at 32500€ (comparably or even larger sized Clio at about 15000€). It used to be possible to buy it cheaper - but then you needed to add monthly rent of the battery pack (battery pack was leased from the manufacturer, you don't buy it with the Zoe - Renault specialty)
So there simply isn't either physical or pricing space for any fancy equipment like extra airbags, electronic safety/assistive systems, etc. - and that's where Zoe was losing big time in the NCAP tests.
"because otherwise it wouldn't be possible to sell it."
Like, Dacia is making their EV literally for 1/3rd of the cost of the Zoe[0], and yet they managed to get 1 star in ncap tests[1]. So no, I don't think it "wouldn't be possible" to include these better systems - it's just Renault being cheap and riding their brand recognition as Zoe is a pretty popular model.
[0] https://www.autocar.co.uk/car-news/new-cars/dacia-spring-ev-...
Dacia certainly didn't get that one star because it includes any assistive systems (it does not). It is just slightly bigger so the protection of the occupants in the cabin is naturally better than in the cramped Zoe.