Someone else might know the answer. But some programs do (with or without notification on the program installer) also install junkware. This might be toolbars or something else. When that happens, often the default browser homepage is changed also.

Why is a good question. Sometimes the people who develop the main program receive kickback payments if they include junkware with their program. I refer to such extras as junkware. Adobe got into strife with its users when it included Growl within their CS5 product installer range. Growl Installation with Adobe CS5 « Adobe Installation and Licensing. However they quickly responded on how to remove it due to customer backlash.
The programs that choose to include junkware with their program installer, sometimes notify in the installer these extras will be installed, but not always, such as in Adobe's case. Sometimes it is the default that these junkware will be installed. We pressured FrostWire into at least not having their junkware set as default for installation. We complained they even had junkware with their 4.20 & 4.21 installers. File_Girl produced junkware free versions instead for this forum lol.

Yes, lots of programs include things you don't want and usually don't know about. Quick Time seems to be included in just about everything I download. Google Chrome gets packaged with other programs. Many times they will give you the option of not receiving the added stuff - unchecking a check box usually does it.

But not always. I have heard that if you download the software version of AOL, you will have at least seventeen programs put on your computer without your ever even knowing they are there.

I have had donwloaded programs change my homepage, but never in a way that I wasn't able to fix it with several mouse clicks. It is easy to restore your desired homepage if some program decideds to change it, PROVIDED the change is not a hijack.

A homepage hijack is something else altogether. When a hijack happens, you cannot change your homepage back; you are stuck with the new version. It is possible to get your original homepage back, but you don't ever want to have to do what it takes to get this done. There are Web sites dedicated to helping people through the complicated steps that have to be taken to cure a homepage hijack.

I can understand why progarms would included junkware in their downloads. I can't understand why they would hijack a homepage. All hijacking accomplishes is creating mega tons of anger toward the program that caused it in the first place. If they think they are getting advertising, they should think again. All they are getting is hatred and a guarantee that no one will utilize whatever service they have to offer.