It's more than that; it's to provide additional capacity to the cryptocurrency 'inter-net'. A single blockchain cannot physically scale beyond a certain number

It's more than that; it's to provide additional capacity to the cryptocurrency 'inter-net'. A single blockchain cannot physically scale beyond a certain number of transactions (based on Amdahl's law), but the amount of value that passes through a single network can in fact keep going up indefinitely (e.g. when the price of the coin goes up, the value of transactions go up, even though the actual number of transactions stay the same) - But the flat transaction fees become prohibitively high and only suitable for large transactions; that's why you need new networks with lower-priced coins and fees to handle the load of smaller transactions.