What are other layer 2's besides lightning and why aren't they catching on?
There’s @Blockstream liquid, which is really a side chain. It’s privacy focused and has Tether built into its 1 minute blocks.
Ark https://ark-protocol.org/ it's not really competition for lightning but could probably take over the bulk clearinghouse elements of lightning and enable further savings on block space usage... it's more like SWIFT versus Visa ark as to lightning