Well, mate, Bitcoin and SPV can scale to a certain extent.

Bitcoin's block size and block time limit the number of transactions it can process per second. That's where scalability issues come in.

As for SPV, it allows users to verify transactions without downloading the entire blockchain. It makes running a Bitcoin client less resource-intensive, but it doesn't increase Bitcoin's transaction throughput.

So while they help in some ways, they don't fully solve the scalability issue on their own. That's why other solutions like Lightning Network are being developed.