There have also been few successful secessionist movements that weren't backed by force of arms.
Anyway, I think the calculus is unique in this case. We are already seeing major companies move their headquarters out of Catalonia. Catalonia's independence would mean disruption of access to EU common market benefits and Schengen. Also they couldn't stop smaller provinces from voting to rejoin Spain.
They see it as "payback" for the EU/Nato's support for Kosovo's unilateral declaration of independence. Interestingly, Spain is probably the only Western nation that doesn't recognize Kosovo's independence.
I won't split hairs with you on that, but -- right or wrong -- Spain's Constitutional Court ordered the referendum stopped, and the Spanish government moved to enforce that order.
That probably would have been the better move as far as "optics" are concerned, but the Spanish constitution states that this kind of referendum is illegal.
In any case -- I think the ruling party in Spain wanted this to flare up so they could consolidate political support during the next election, since most of Spain is adamantly opposed to Catalan independence.
For better or for worse, there will be no independent Catalonia in the foreseeable future. About 40-50% of Catalans don't support this. The EU doesn't support this, no Western nation supports this (save maybe Russia if you consider them Western -- and even their position is unclear). Furthermore, Spain won't allow it, and they're the main actor in a position to do something about it.
Even if Catalonia somehow manages to enforce its declaration, the economic consequences will be so devastating that they will reverse course in due time.
Anyway, I think the calculus is unique in this case. We are already seeing major companies move their headquarters out of Catalonia. Catalonia's independence would mean disruption of access to EU common market benefits and Schengen. Also they couldn't stop smaller provinces from voting to rejoin Spain.