They have more economic relations with the rest of the CET countries combined, so it’s more beneficial to stay in the same time zone.

Is that not true for Portugal, or Finland in the other direction for example? I haven’t seen clear reasons for why a 1-hour offset would seriously affect economic relations particularly if it doesn’t affect when businesses are operating. Spain is already known (in stereotypes, so not sure if this holds up in reality) for later start/end times to the workday or other engagements than most western/central European countries, probably partly a figment of the time zone.