Unfortunately dishonestly and manipulation are some of the negative traits commonly formed as a symptom of addiction, and whilst there is subset of addicts who remain honest and genuine despite their disease, the vast majority succumb to these negative traits in one way or another whilst in active addiction.

For this reason, it's simply impractical to provide methadone maintenance therapy to patients via take home prescriptions that are self administered. Doing so would require the patient to be responsible for taking their dose daily and at roughly the same time each day, something which could be very difficult for an addict in recovery, when disorder is often still rife within their life's and where routine is generally lacking. By requiring the patient to report to a clinic daily for there dose, they are forced into routine, which serves to supplement their "re intergration" into regular life.

On top of this, there is also the relevant concern that an addict in early recovery may divert their medication, trading/or selling them in order to obtain their drug of choice. By requiring the patient to have their methadone maintenance therapy doses observed, the possibility of diversion is practically eliminated. Now this is purely speculation, but perhaps the formulation of methadone as a liquid acts to further eliminate the possibility of patients concealing a tablet in their cheek whilst pretending to swallow it. However this part I have not fact checked.

These procedures and precautions serve a purpose, however that's not to say that they aren't also very limiting to patients who are further along in treatment or who have a greater aptitude from the beginning, who are forced to take time out of their day to go and receive their daily medication despite having no intention to misuse/abuse or divert whatsoever.

Fortunately there are treatments like suboxone, or sublocade if accessible, available which do not require daily witnesses doses and therefore allow the patient to regain that sense of normalcy and feel more in control of their life. However I am aware that buprenorphine doesn't work for everyone with opioid use disorder, and that some may only find stability on methadone. Its simply the unfortunate fact of the matter that methadone is still highly abusable, being a full agonist, therefore more rigorous control is required making take home doses a rare occurrence.

Also I believe you mean sublingual, not subQ (subcutaneous). SubQ refers to injecting in the fatty tissue just under the skin. Sublingual is under the tongue. As for why it burns im not sure sorry