It's because the TOS of Google Maps only allow you to consume their imagery and maps using their API. See Section 3.2.4 e) from https://cloud.google.com/maps-platform/terms/#3.-license-
(e) No Use With Non-Google Maps. Customer will not use the Google Maps
Core Services in a Customer Application that contains a non-Google
map. For example, Customer will not (i) display Places listings on a
non-Google map, or (ii) display Street View imagery and non-Google
maps in the same Customer Application.
If you don't, you are already doing something risky or maybe illegal (if in a pro context at least)
You can always bypass the limitations by making calls to Google Maps through their JavaScript API and sync the view within OpenLayers, Leaflet or Mapbox.gl (both Kepler.gl and Nebula.js use it). Several libraries does that:
You also need to be aware that Google Maps is also not the cheapest solution as in recent years, the cost to run a web map application using Google Maps skyrockets (moreover now, even for free tiers, you need a credit card). The other sources cost really less and for most cases are enough and in some cases they also are better for example for bike maps when using OpenStreetMap.