You can ask the same for mycelium or bluewallet, why haven't they released a better app for desktop? Why are they just better in mobile mode despite being so popular?
Blue Wallet actually has a desktop app, but they don't highlight it enough on their website. They have big download buttons for their iOS and Android versions and a bit of text mentioning their desktop wallet. There is also a link to the
desktop version at the bottom of the site. Their OS choice is also peculiar. No Linux, no Windows, and only macOS.
I have never used the desktop version of the blue wallet but I have it installed on my mobile.
Also for my desktop, I use electrum and I think that is the best combination, that is Electrum on desktop and Blue Wallet on mobile.
The best thing i like about blue wallet and started using it recently is the read only wallet, where I can watch my bitcoin balance in my wallet on my android phone and feel safe even if my android phone is lost no one can get access to my coins.