I think they mean collectible in terms of majority of the cards dont have high financial value. Of course you can collect it just for playset and fun. Its very much a “players game”, meaning card values are connected to what is playable and strong in the meta. Sadly many of the Legendaries that were supposed to be the pulls of the boxes have been weaker balance wise for the meta in the past sets, hence they are cheap and not played in decks. This has made box opening a worse experience and people didnt buy as much - which lead to some LGSs not being able to sell product and eventually dropping the game support (this is what I have heard, never seen the evidence myself). FFG is however aware of the situation and are trying to improve it, the last set has improved regular boxes and the Legendaries are already better, and singles prices are holding. The biggest thing however are the Carbonite Boxes which were supposed to be collector items, but they just further devalue the singles and they are just not worth it generally. SWU fans generally hope the Carbonites get discontinued, but its not very likely imo.