OK let us compare the two sides of the argument for pro's and cons to see what we have. First we will go with pro's of having a cap on respec costs, and then the cons of allowing it to continue rising indefinitely.
-Caping respec costs-
--Pro's--
-players are more viable. You can switch your role to fulfill what you need, at an affordable cost WHILE NOT being able to "respec willy nilly" as someone put it.
-You can correct mistakes and experiment around with various specs, finding newer, stronger combinations for abilities. People didn't find SL/SL Warlocks in WoW by sticking to the normal builds.
-More players will have an easier time finding instances and groups and doing them successfully. Lets face it, you are not going to complete a flashpoint or heroic area that is at the level of difficulty designed for you if you simply bring 4 dps. That is the point of making a strategic group.
-Playing the same spec, all the time, can get very boring and impede the different modes of gameplay. If you have to play as a DPS marauder all the time you probably wont excel in pvp, you won't be able to off tank, you are restricted to experiencing the game one way. Being able to try and use other specs allows for refreshing gameplay and keeps players (paying customers) around longer.
--cons--
-You lose more credits with each time you respec. You use credits to repair gear, buy new gear, buy consumables, work on professions, really everything. Do you really want to be spending 90k and higher (Since there is no visible cap) JUST to go healer when someone has a RL issue and can't make it to a raid?
-With less people willing to respec, healers and tanks will be in high demand. Most instance and heroic groups will be doomed to either failure, or an eternity in the void of LFG. Because lets face it, without heals and tanks and dps, a group isn't a group, and won't clear even a flashpoint.
-There is a lot less incentive to actually explore the game. You should experiment at some point with all 3 of your classes talent trees, and you should try to find your own style of playing. Having such powerful reasons NOT to change the spec will simply bring into play 1 or 2 specs for each tree that are optimal and used by everyone, similar to how WoW had a very long period of time where SL/SL Warlocks were it for arenas while Shadowbolt-Sacrifice was used in raids. If you weren't SL/SL you did NOT arena. If you weren't SB-Sac spec, you didn't raid. Oh and, lets face it. Once you have seen the story once, it is not as good the second time through. Leveling alts and other character classes is NOT a fun idea for most people some enjoy it, the majority like focusing on that which they love and are good at. If it is simply required to have at least 1 healing character, 1 DPS character, and 1 tank character in order to have viable options most people are going to ditch out. Grinding the gear and levels, and doing the same story multiple times to do so, are really just tedious and this takes the fun out of even a Star Wars story. Similar to how yall killed off Chewie.
-3 to 1 there IS a maximum amount of credits you can have on you at one point and time. If the max credits is 999,999 then eventually it will cost you 999,999 credits JUST to respec. This idea alone is ludicrous.