The Just Procure Lockheed thing is never heard around JPL. I'm not doubting that someone said it, some time, but that's not the Lab mindset at all. If you want to make an institutional characterization about JPL, you could say "hardware-centric", or "arrogant", or "cocky", but not "Just Procure Lockheed".
I agree that there are a lot of subs, but JPL and other centers have a very strong interest in maintaining a core capability in strategic areas. Launch vehicles: not a core capability, and commercially available -- subcontract these. Planetary robotics and deep space communication: core capabilities -- keep in-house.
Also, your comment underestimates how much distributed expertise is required to develop and integrate a set of instruments like this, and to get it to Mars. It's not practical for all that expertise to be NASA only.
I recently saw a lecture on a proposal for an upcoming space mission and the speaker mentioned the contractors at Lockheed working on the proposal several times. I remember because it kind of stood out to me that they're involved from the start.
A lot of large launches are done by United Launch Alliance (ULA), which is a Boeing/Lockheed-Martin consortium. (I.e., they provide the rocket and the launch facilities -- for instance, they did all the Shuttle launches, as well as the MSL launch.) You'd have to involve them at an early stage to get costing worked out.
There's a second consortium, also Boeing/Lockheed-Martin, that does manned space operations for Shuttle (formerly) and for Station. (Operations = flight control from the ground, post-launch. E.g., rotating the solar panels on Station.) That one is called United Space Alliance, or USA for short. Catchy, no? ;-) AFAIK, USA does not play any role in unmanned operations.
As the GP pointed out, there is a lot of money in launches, launch vehicles, and in manned operations, hence the contractor involvement. As you can guess -- you can't even play Boeing off against Lockheed-Martin because they're in a consortium -- that world is kind of creaky. SpaceX is disrupting ULA big-time.
Lockheed-Martin is also involved in instrument design and other non-launch activities. Getting an instrument into space is a multifaceted affair.
Here's a good example. Juno, a spacecraft currently on its way to Jupiter:
Managed by JPL, spacecraft by Lockheed-Martin, science PI is at SWIRI, instruments from all over. And this is a "medium-size" mission, not a "flagship" mission like MSL or James Webb.
I agree that there are a lot of subs, but JPL and other centers have a very strong interest in maintaining a core capability in strategic areas. Launch vehicles: not a core capability, and commercially available -- subcontract these. Planetary robotics and deep space communication: core capabilities -- keep in-house.
Also, your comment underestimates how much distributed expertise is required to develop and integrate a set of instruments like this, and to get it to Mars. It's not practical for all that expertise to be NASA only.