it is mainly because most of the wallets that are referred to as SPV are actually connecting to a centralized server rather than connecting to actual bitcoin nodes using features such as bloom filters. (Electrum is in between, you connect to nodes but the nodes have to be "special" nodes that have a separate index). so practically the choice is limited to only 1 server, the one that the wallet company runs.

but this could partly be because nobody has wanted the feature yet. usually people who go for an SPV wallet don't have the capability or willingness to run their own full node. you can always find your favorite wallet's developers and request the new feature though.