The way I see it, players not engaging with a game could fall under the following scenarios:
1. The GM's fault. They are not describing things well. Or they are taking away the PCs ability to affect the setting via GMPs or other similar problems. (I don't think this is the OPs issue, just listing for completeness.)
2. The players do not want to engage with the world. This can be due to a variety of factors from being too picky about setting, having very specific expectations about the game, etc.
3. The players do want to engage with the setting but are not really sure when or how to do that. When they hear you describe a room they think that is everything there is to know, they don't think to ask if they can investigate further, they don't have those habits and expectations. (This is the situation I was originally addressing.)
4. They do want to engage with the setting but they have trouble visualizing what is going on. We had been playing for years using Theater of the Mind. Then one day we were using some maps and pins to indicate character location for a quick dungeon crawl game to show another person how to play D&D. Afterwards he came up to me and told me how much easier it was for him to see it on a map, he had been struggling for years with the Theater of the Mind game play. Since then I have put a lot more effort into maps and visualization.
5. They do want to engage but are distracted. The dreaded phone at the table problem. Online this can be even worse as there is a browser right there and it is so tempting... Many players think they can multitask roleplaying and surfing the web, or what ever, they can't. They do believe that they are participating just like everyone else. Also, many players need something to keep their hands busy, this isn't a malicious thing but they sometimes do need to be asked to pay closer attention. This can be a difficult conversation to bring up.
I can't tell you which problems the OP is experiencing, and there are probably some I missed, only the OP can answer that question.
I don't know what to do about #2 above. I have never had to deal with that sort of player.
For #4 and #5 I would suggest maps, minis, visual aids, music, sounds, etc. I would also suggest "always on initiative" ie rotating around between your players and asking them what they do next so that everybody gets a chance at equal screen time. There are probably plenty of other GM best practices that can help with this sort of thing. And as always, talk to your players.
^2