Mojang needs to keep things simple, functional and consistent for the vast majority of their players. They choose the best defaults that work for the most number of people.
Also, modded players will let you know just how badly Optifine breaks rendering calls. The first step of any troubleshooting is checking if Optifine is installed.
I use MCPELauncher to run the Android version under Linux, which lets me play with my son on his Switch.
As you've observed it's revenue-generating in a way the Java Minecraft is not, and it provides a controlled experience.
Microsoft has been talking to influential people about how to land some sort of modding-lite to Bedrock. I suspect that won't go well, but in principle it could work. They've been showing where they're going to people like Direwolf20 (popular Youtuber and small modder)
Actual (Java) Minecraft modding involves two layers of effort. Firstly, since Minecraft is Java, a layer is using Java's own introspection to reach inside Minecraft's core systems and genericise them. For example Minecraft doesn't really grasp "fluids" as a general group, it has a bunch of special cases for water, lava... but a mod might want to add others (Molten steel, Goat milk, Diesel, Tritium... all real examples of fluids in common mods) and then the second layer needs to add generic capabilities - if all you really have is lava and water but with different textures that's lame, but if new fluids have density and temperature and so on they can interact even without custom code for specific behaviour. Knowing Goat's milk is the same temperature as water my Seebeck Effect generator won't work if you put goat's milk on one side and water on the other. "Liquid Helium" however at 3K rather than 300K would work well, and "Molten steel" at 1800K would help on the other side, even without my Seebeck Effect Generator mod knowing what these liquids actually "are" in any sense.
I do not see an appetite at Microsoft for this level of detail in Bedrock Mods. I'm expecting some basic customisability, but nothing comparable to, say, AE2 or Thaumcraft (sprawling mods that touch every part of Minecraft).