Before trying to answer your questions, I have to note a problem in the fundamental basis of the question:
If your boat has only a two-position switch, the switch CANNOT be a Cole-Hersee M532 switch, because a Cole-Heresee M532 is a three-position switch used extensively to control navigation lighting. A properly wired M532 switch will have three positions: OFF, AT ANCHOR, UNDERWAY.
A switch similar in appearance would be a M531, which is a three-position switch but not useful for controlling navigation lighting unless the lamps for UNDERWAY and AT ANCHOR are completely separate lamps.
A real Cole-Hersee M-532 is a bit tricky to wire. For help with wiring see the article in REFERENCE at
Navigation Lamp Wiringhttp://continuouswave.com/whaler/reference/navLightSwitch.htmlContinuing further with the assumption your particular Boston Whaler boat has a two-position switch ON-OFF switch to control navigation lighting and that switch is an OEM installation, then to answer your question about the reason for Boston Whaler to choose that type switch is going to be extremely difficult to answer. I doubt anyone remains with Boston Whaler from 1972 (48-years ago) who could answer authoritatively about the company's intent by use of a simple ON-OFF switch, if they indeed did produce the boat in the configuration it has now.
On boats that have been away from the factory for 48-years, there is not a reasonable basis to presume that all electrical wiring on the boat remains precisely as it was when the boat left the factory, or even if there was any of the wiring in place when the boat left the factory. It is very common that in 48-years of use someone may have changed or added something.
Another reasonable corollary question: do you really need to show a White All-Round light when at anchor in a 13-foot boat?
Please see the USCG Rule at RULE 30, paragraph (e):
(e) A vessel of less than 7 meters in length, when at anchor, not in or near a narrow channel, fairway or anchorage, or where other vessels normally navigate, shall not be required to exhibit the lights or shape prescribed in paragraphs (a) and (b) of this Rule.
If you really need a three position switch, buy an actual M532 and re-wire as shown in the article linked above.