I notice that AA has put on many new flights for their MIA to Western US routes. This is to attract cruisers; however, the seats have not been filled and likely there will be cancelled flights. This practice is a pain to travellers who try to pick a convenient flight only to be cancelled out at the last minutle. What benefit is this? Certainly not to the traveller, and the carrier has to redo everyone's reservation. I have found this only on AA. What can be done to stop this?

I can't speak for the cancelled flights, but I wish AA would offer a non stop flight several times a week out of my market to MIA. You've already mentioned the crusiers, but MIA is also a gateway to the Caribbean for AA and other airlines. It's too bad you've had frustrating experiences. Write/call AA regarding your frustrations, though I doubt it will do much good. AA will determine how they operate their routes and what's profitable/adds competitive value. Great airline by the way.

Airlines don't cancel flights just because...

Urban legend.

And I don't know where you get your info from but it seems like most MIA-LAX non-stops tomorrow are either close to being sold out or are in fact overbooked:

<i>American Airlines
Flight: 1247
Departs
Miami (MIA)
6 January
7:50 Arrives
Los Angeles (LAX)
6 January
13:30 Notes
Cabin class: F1 A1 P0 Y2 B0 H0 K0 M0 L0 W0 V0 G0 S0 N0

American Airlines
Flight: 1018
Departs
Miami (MIA)
6 January
18:20 Arrives
Los Angeles (LAX)
6 January
21:05 Notes
Cabin class: F0 A0 P0 Y2 B2 H0 K0 M0 L0 W0 V0 G0 S0 N0

American Airlines
Flight: 1125
Departs
Miami (MIA)
6 January
21:15 Arrives
Los Angeles (LAX)
7 January (Next day)
0:05 Notes
Cabin class: F0 A0 P0 Y1 B0 H0 K0 M0 L0 W0 V0 G0 S0 N0

American Airlines
Flight: 299
Departs
Miami (MIA)
6 January
8:15 Arrives
Los Angeles (LAX)
6 January
10:50 Notes
Cabin class: F0 A0 J0 D0 I0 Y0 B0 H0 K0 M0 L0 W0 V0 G0

American Airlines
Flight: 283
Departs
Miami (MIA)
6 January
11:05 Arrives
Los Angeles (LAX)
6 January
13:50 Notes
Cabin class: F0 A0 P0 Y0 B0 H0 K0 M0 L0 W0 V0 G0 S0 N0 </i>

and San Francisco:

<i>American Airlines
Flight: 431
Departs
Miami (MIA)
6 January
8:10 Arrives
San Francisco (SFO)
6 January
11:25 Notes
Cabin class: F0 A0 P0 Y0 B0 H0 K0 M0 L0 W0 V0 G0 S0 N0

American Airlines
Flight: 1455
Departs
Miami (MIA)
6 January
14:55 Arrives
San Francisco (SFO)
6 January
18:10 Notes
Cabin class: F0 A0 P0 Y0 B0 H0 K0 M0 L0 W0 V0 G0 S0 N0 </i>

Prolly b/c huge cruise ships return to Miami on Sundays.

I checked MIA-LAX 1/6, 1/7 and 1/8 and it's pretty much the same. Few more F seats availibility but that's about it.

As many people have pointed out here, AAFF among them, airlines evaluate the viability of all their routes from season to season and year to year, and add and subtract as needed. But they don't cancel individual flights at their whim because there aren't enough passengers. They have contracts to transport cargo on those flights, and they have to meet those. A crew on any given flight has to be in place for another scheduled flight that will depart the destination airport.

Barring mechanical problems, or weather, or flight crews that can't get there because of mechanical problems or weather at other airports, your flights should operate as scheduled.