Why do not do just a SHA256(SHA256(…ALL TXs IN A COMPACT WAY…)) these days ?
Even supposing the idea of your query (that the usage of the Merkle construction is needless) is correct, this is not one thing that may simply be modified.
Converting how block headers decide to transaction information could be an overly invasive alternate, which might be a difficult fork, however would additionally simply damage actually each piece of Bitcoin device ever written. Except now not converting this implies a near-fatal worm for Bitcoin, this is not even price discussing.
This is not even that. Concatenating the hashes as a substitute of the usage of a Merkle tree is perhaps a couple of milliseconds speedup in line with block, on susceptible {hardware}.
I do know Skinny nodes are doing this
Sure.
however this can be a little bit needless since primary branches are required.
I do not know what this implies.