@WadeGDouglas In short, because the ACH process that all checks, including eChecks, use is different from the credit card process. There is no instant authorization -- rather, checks are submitted through the ACH network for clearance, and the customer's financial institution either honors the check or doesn't. In cases of mismatches, it's not uncommon for the financial institution to honor the check regardless, upon identifying the correct account, and submitting a Notice of Change (NOC) to inform the merchant of the correct account information. Therefore, the routing number is the far more important number to get right.
We're required by NACHA policy to only accept valid ABA routing numbers, which are assigned to individual financial institutions. But since the system has alternate means to ensure payment is successful, account verification is not an option.
This and more is touched upon in the eCheck.Net Users Guide.
That said, there are third-party check verification services, but we do not currently support those -- although I cannot rule anything out for the future.
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"Move fast and break things," out. "Move carefully and fix what you break," in.