Maybe, but I think you can make a case for the opposite too. Without exchanges, there'd be no crypto. Exchanges are the only reason 99% of people who have crypto can figure out how.

Especially with mobile devices taking over. An increasing number of people don't even have a laptop or desktop to hold a whole blockchain on. Even an iPhone 13 Pro with 1TB of storage would lose 10-20% of its space to that. That isn't going to improve. The more popular it gets, the faster it grows, and it would compete with all the other storage needs that also grow.

Get someone to load up and maintain a whole blockchain on their 1TB phone, and you lose them the moment they need more room for photos or offline synced music and files.

Not everyone needs a full copy of the blockchain to run a node.

A pruned full node downloads and validated all blocks, then discard everything not relevant to its own wallet.

A variety of “light clients” are also available for most chains, which fetch transaction data from peers as needed (usually using something like bloom filters to increase privacy).

Most ethereum apps just go through Infura. That’s a horrible centralized single point of failure that I’m not advocating, but the point is there are many ways a wallet app can connect to a remote full node.

not sure about how big the ETH blockchain is, but the bitcoin blockchain fits in under 6GB if you enable prune mode. I still wouldn't run a full node on my phone, but disk space isn't the limiting factor.

Agreed. And even if the storage issue isn't the main blocker, there's also energy usage, bandwidth, security and usability issues when it comes to phones.