One long walkway along the entire central London stretch of the Thames

The Thames is so lovely when the weather's nice, why is it that there aren't walkways all the way along it?

So many countries make the most of their waterside space with boardwalks and promenades littered with cafes, restaurants, and green spaces. Does anyone else wish there was a walkway all the way along it, rather than the sporadic walkways which require dipping back inland occasionally to walk along roads, under tunnels, and through back alleys.

I wonder how much it would cost to add some and how much it'd bring in in additional tourism revenue.

Does anyone else ever think this?