Developers of newer versions of a system even if it is a migration from TUI to a Web GUI should really strive to maintain the shortcuts and hotkeys, an upgrade its suposed to be "that", extra functionality not a replacement of the existing one. Sadly there is this assumption that given it has a GUI there is no need of shortcuts or hotkeys, forcing users to use the mouse.
Gmail does provide some hotkeys and I think even those "few" ones really help, also Atlassian applications yet most web pages I have interacted with have none
Part of the problem here is that desktop development frameworks included keyboard shortcuts essentially for free: Mac associates them with menu items, emacs/vim's key -> command -> action design give an obvious place to implement shortcuts; Delphi and similar programs had similar places to automatically slot in keyboard shortcuts. Web frameworks focus on visuals and mouse interactivity and keyboard control is almost an afterthought (aside from some minimal attention to tab-order because of accessibility).
Another part of the problem is that the contents of the browser is mostly untrusted, and the browser itself already has a giant pile of shortcut keys that would conflict.
Gmail does provide some hotkeys and I think even those "few" ones really help, also Atlassian applications yet most web pages I have interacted with have none